DISEASES OF THE PERIPHERAL NERVES.
BY FRANCIS T. MILES, M.D.
The nervous system of the higher animals is the apparatus by which stimuli coming from the external world or originating in the interior of their own bodies are perceived (its sensitive functions), or cause muscular contraction (its motor functions), or, lastly, cause molecular changes in tissues (its trophic functions).
Besides this power which the nervous system possesses of receiving impressions originating outside of itself and actively replying to them, it appears also to possess the power of originating within itself changes the result of which are sensations, movements, and trophic alterations. In other words, it can act automatically.
The apparatus for the performance of these various functions consists of the end-organs, the nervous centres, and the nerves.
The end-organs are peripheral mechanisms for the reception of impressions. The structure and mode of action of some of them, as the eye and the ear, are pretty well understood, while others, as those connected with the sense of touch, temperature, etc., are but imperfectly known. It is probable that there are also peripheral mechanisms which facilitate the delivery of the impulses coming from the nerve-centres to the organs, tissues, muscles, glands, etc.
The nervous centres are made up of nerve-cells variously connected with each other. They are immediately concerned in receiving impressions conveyed to them by the nerves and transforming them into sensations, or transmitting them to other organs, causing reflex actions, or in originating sensations and impulses.
The nerves are organs which, connected at one extremity with the end-organs and at the other with the nervous centres, convey peripheral impressions to the centres, and impulses and influences from the centres to the various organs of the body.
As it is with diseases of the peripheral nerves that we are now concerned, let us begin by looking more closely into their structure and functions.
The nerves appear to the naked eye as white strands of variable size, which a close inspection shows to be made up of threads or fibrils (best seen when the cut end of a nerve is examined) bound together by fine connective tissue and scantily supplied with blood-vessels. A microscopic examination shows that each of the fibrils visible to the naked eye is made up of a great number of fibres. These are the medullated nerve-fibres, and they extend unbroken between the nerve-centres, with the cells of which they are connected, to the various organs and tissues, with which they also enter into organic union.
If we examine the structure of a medullated nerve-fibre, we find it to consist of a central thread called the central axis or axis-cylinder, in which close microscopic investigation shows a longitudinal striation, indicating that it is made up of fibrillæ. Surrounding the central axis like a sheath is the white substance of Schwann, composed of an oleo-albuminous substance, myeline, to which the nerves owe their white appearance. According to some observers, the white substance of Schwann is pervaded by a meshwork of fibres. Surrounding the white substance of Schwann is the sheath of Schwann, a structureless membrane having at intervals upon its inner surface nuclei, around which is a small amount of protoplasm.
At intervals along the course of the nerve-fibres are seen constrictions which involve the sheath and white substance of Schwann, but which do not affect the central axis, which passes unbroken the points of constriction. These are the nodes of Ranvier. Each space on the fibre beneath the nodes of Ranvier contains one of the nuclei of the sheath of Schwann, and probably, together with the white substance of Schwann, represents a cellular element. Diseased conditions sometimes respect the limits of these cellular elements.
The central axis is the true conducting part of the nerve-fibre, and it is probable that each of the fibrillæ of which it is composed has a separate peripheral termination and possesses the power of isolated conduction. The white substance of Schwann and the sheath of Schwann protect the central axis and seem to be connected with its nutrition.
The fibres in a nerve are bound together by loose connective tissue, the endoneurium, into the primitive bundles, which are again united by the perineurium, a membrane of laminated connective tissue, into more definite funiculi seen by the naked eye, the secondary bundles.
The secondary bundles are tied together by connective tissue, in which are found fat-cells and in which run the fine blood-vessels supplying the nerves. This connective tissue has been named the epineurium, and its condensed outer layers constitute the sheath of the nerve. It is important to observe that the connective tissue of the nerves is permeated by lymphatics which penetrate to the nerve-fibres, so that these are brought in contact with, and as it were, bathed in, the lymph.
Each nerve-fibre runs an isolated course from end to end, without anastomosing with other fibres, and near its peripheral termination it usually divides into two or more branches.
The fibres of the peripheral nerves depend for their integrity and nutrition upon their connection with central organs. The large multipolar cells of the anterior horns of gray matter of the spinal cord preside over the nutrition of the motor fibres; the ganglia on the posterior roots of the spinal nerves over the nutrition of the sensitive fibres.
If a nerve be severed from its connection with these centres of nutrition, it in a short while undergoes degenerative changes which result in complete destruction of its fibres.
The nerve-fibres when in a state of functional activity conduct impressions along their length to the end-organs or to the nerve-centres with which they are in connection. This property of the fibres we call their conductivity. Each fibre conducts impressions in an isolated manner, not communicating them to other fibres with which it may be in contact. The rapidity of this conduction in human nerve-fibres is estimated at 33.9 meters (about 38 yds.) per second. This rate may be diminished by cold or by the anelectrotonic condition which is induced in the nerve by the passage through it of an electric current.
The nerve-fibres are irritable; that is, the application to them of stimuli excites their functional activity, and the impression made by the stimulus is transmitted to their extremities.1
1 The nerve-fibres in man do not appear to attain their full irritability until the fifth or tenth month after birth (Soltman).
The natural or physiological stimuli of the nerves act upon their extremities. Either they act through the peripheral mechanisms, giving rise to impressions which are conducted centripetally to the cells of the nerve-centres and there cause sensations or reflex actions, or they act upon the nerve-centres, giving rise to impulses which are conducted centrifugally and cause the various phenomena of contraction of muscles, inhibition of contraction, secretion, etc. Besides the physiological, there are other stimuli which excite the functional activity of nerve-fibres when applied at any point along their course.
Mechanical stimuli, blows, concussions, pressure, traction, etc., excite the nerves, causing sensations when applied to sensitive nerves, or contraction of muscles when applied to motor nerves. When mechanical stimuli are pushed farther, the irritability of the nerves may be destroyed. The gradual application of mechanical stimuli may destroy the irritability of nerve-fibres without any exhibition of excitation, as in paralysis from pressure. In nerve-stretching it is probable that many of the results depend upon the mechanical stimulation of the nerve-fibres by the traction. With a certain amount of force used the irritability of the nerve may be increased; carried farther, both the irritability and the conductivity may be diminished, and finally destroyed. As the centripetal fibres are soonest affected in the stretching, we can see how this proceeding is most beneficial in neuralgias, where a potent factor, if not the cause of the disease, is an abnormal excitability of the nerve-fibres. It is to be observed, nevertheless, that in cases of continued pressure upon mixed nerves the motor fibres are the first to suffer loss of their conductivity.
Sudden alterations of temperature act as stimuli to nerves. Heat increases their irritability, but its prolonged application diminishes it. Cold in general diminishes the nervous irritability, and may be carried to the point of completely destroying it temporarily.2
2 But at a certain age in freezing the ulnar nerve Mitchell found its irritability notably increased.
Many substances of widely-different chemical constitution, as acids, alkalies, salts, alcohol, chloroform, strychnine, etc., act as stimuli when applied directly to the nerves, apparently by causing in them rapid molecular changes. Also may be enumerated as chemical stimuli to the nerves substances found naturally in the body, as bile, bile salts, urea. The rapid withdrawal of water from nerve-tissue first increases, and then diminishes, its irritability. The imbibition of water decreases nervous irritability.
An electric current of less duration than the 0.0015 of a second does not stimulate the nerve-fibres. It would appear that more time is required for the electric current to excite in nerve-tissue the state of electrotonus which is necessary to the exhibition of its functional activity. The electric current stimulates a nerve most powerfully at the moments of entrance into and exit from the nerve, and the more abruptly this takes place the greater the stimulation. Thus the weak interrupted currents of the faradic or induced electricity owe their powerfully stimulating effects to the abruptness of their generation and entrance into and exit from the nerves. At the moment of the entrance of the electric current into the nerve—that is, upon closing the circuit—the stimulating effect is at the negative pole or cathode; when the current is broken—i.e. leaves the nerve—the stimulating effect is at the positive pole or anode. A current of electricity very gradually introduced into or withdrawn from a nerve does not stimulate it. But if while a current is passing through a nerve its density or strength be increased or diminished with some degree of rapidity, the nerve is stimulated, and the degree of stimulation is in proportion to the suddenness and amount of change in the density or strength of the current. Although with moderate currents the stimulation of the nerve takes place only upon their entrance and exit, or upon variations of their density, nevertheless, with a very strong current the stimulation continues during the passage of the current through the nerve. This is shown by the pain elicited in sensitive nerves, and the tetanic contraction of the muscles to which motor nerves are distributed.
An important factor in electrical stimulation is the direction of the current through the nerve. A current passed through a nerve at right angles with its length does not stimulate it. Currents passing through a nerve stimulate in proportion to the obliquity of their direction, the most stimulating being those passing along the length of the nerve. Motor nerves are more readily stimulated by the electric current the nearer it is applied to their central connection. Experiments on the lower animals would seem to indicate that the motor fibres in a nerve-trunk do not all show the same degree of irritability when stimulated by the electric current.
The irritability of the nerve-fibres may be modified or destroyed in various ways. Separation of nerves from their nutritive centres causes at first an increase of their irritability, which is succeeded by a diminution and total loss, these effects taking place more rapidly in the portions nearer the nerve-centres. It is important to observe that an increase of irritability preceding its diminution is generally observed in connection with the impaired nutrition of nerves, and is the first phase of their exhaustion.
Prolonged and excessive activity or disuse of nerves causes diminution of their irritability, which may go to the extent that neither rest in the one case nor stimulation in the other can restore it. If a galvanic current is passed through a nerve in its length, the irritability of the fibres is increased in the region of catelectrotonus—viz. in the part near the cathode—and diminished in the region of anelectrotonus—viz. in the part near the anode. Certain substances, as veratria, first increase and then destroy the irritability of the nerves; others, as woorara, rapidly destroy it.
The fibres of the peripheral nerves are divided into two classes: first, those which conduct impressions or stimuli to the nerve-centres, the afferent or centripetal fibres; and, secondly, those which conduct impulses from the centres to peripheral organs, the efferent or centrifugal fibres. Belonging to the first class are (1) sensitive fibres, whose stimulation sets up changes in the nerve-centres which give rise to a sensation; (2) excito-motor fibres, whose stimulation sets up in the nerve-centres changes by which impulses are sent along certain of the centrifugal fibres to peripheral end-organs, causing muscular contraction, secretion, etc. Belonging to the second class are (1) motor fibres, through which impulses are sent from the nerve-centres to muscles, causing their contraction; (2) secretory fibres, through which impulses from nerve-centres stimulate glands to secretion; (3) trophic fibres, through which are conveyed influences from the centres, affecting the nutritive changes in the tissues; (4) inhibitory fibres, through which central influences diminish or arrest muscular contraction or glandular activity. No microscopic or other examination reveals any distinction between these various fibres.
Every nerve-fibre has the power of conducting both centripetally and centrifugally, but the organs with which they are connected at their extremities permit the exhibition of their conductivity only in one direction. Thus, if a nerve-fibre in connection with a muscle at one end and a motor nerve-cell at the other be stimulated, although the stimulus is conducted to both ends of the fibre, the effect of the stimulus can only be exhibited at the end in connection with the muscle, causing the muscle to contract. Or if a fibre in connection with a peripheral organ of touch be stimulated, we can only recognize the effects of such stimulation by changes in the nerve-cells at its central end which give rise to a sensation.
When we consider the extensive distribution and exposed position of the peripheral nerves, their liability to mechanical injury and to the vicissitudes of heat and cold, we cannot but anticipate that they will be the frequent seat of lesions and morbid disturbances. It may be that not a few of their diseased conditions have escaped observation from a too exclusive looking to the central nervous system as the starting-point of morbid nervous symptoms. This occurs the more readily as many of the symptoms of disease of the peripheral nerves, as paralysis of muscles, anæsthesia, hyperæsthesia, etc., may equally result from morbid conditions of the brain or spinal cord, and not unfrequently the peripheral and central systems are conjointly affected in a way which leaves it doubtful in which the disease began or whether both systems were simultaneously affected.
The elucidation of such cases involves some of the most difficult problems in diagnosis, and requires not only a thorough acquaintance with the normal functions of the peripheral nerves, but also the knowledge of how those functions are modified and distorted in disease.
The symptoms arising from injuries and diseases of the peripheral nerves are referable to a loss, exaggeration, or perversion of their functions, and we often see several of these results combined in a single disease or as the result of an injury.
The fibres may lose their conductivity or have it impaired, causing feebleness or loss of motion (paralysis), or diminution or loss of sensation (anæsthesia). Or there may be induced a condition of over-excitability, giving rise to spasm of muscles and sensations of pain upon the slightest excitation, not only from external agents, but from the subtler stimulation of molecular changes within themselves (hyperæsthesia). Or diseased conditions may induce a state of irritation of the nerve-fibres, which shows itself in apparently spontaneous muscular contraction or in sensations abnormal in their character, and not corresponding to those ordinarily elicited by the particular excitation applied, as formication or tingling from simple contact, etc. (paræsthesiæ), or in morbid alterations of nutrition in the tissues to which the fibres are distributed (trophic changes).
If we could recognize the causes of all these varied symptoms and discover the histological changes invariably connected with them, it would enable us to separate and classify the diseases of the peripheral nerves, and give us a sound basis for accurate observation and rational therapeutics. But, although the progress of investigation is continually toward the discovery of an anatomical lesion for every functional aberration, we are still so far from a complete pathological anatomy of the peripheral nerves that of many of their diseases we know nothing but their clinical history. We are therefore compelled in treating of the diseases of the peripheral nerves to hold still to their classification into anatomical and functional, as being most useful and convenient, remembering, however, that the two classes merge into each other, so that a rigid line cannot be drawn between them, and that such a classification can only be considered as provisional, and for the purpose of more clearly presenting symptoms which we group together, not as entities, but as pictures of diseased conditions which may thus be more readily observed and studied.
It is well to begin the study of the diseases of the peripheral nerves by a consideration of nerve-injuries, because in such cases we are enabled to connect the symptoms which present themselves with known anatomical alterations, and thus obtain important data for the elucidation of those cases of disease in which, although their symptomatology is similar, their pathological anatomy is imperfectly or not at all known.
Injuries of the Peripheral Nerves.
If the continuity of the fibres of a mixed nerve be destroyed at some point in its course by cutting, bruising, pressure, traction, the application of cold, the invasion of neighboring disease, etc., there will be an immediate loss of the functions dependent on the nerve in the parts to which it is distributed. The muscles which are supplied by its motor fibres are paralyzed; they no longer respond by contraction to the impulse of the will. No reflex movements can be excited in them either from the skin or the tendons. They lose their tonicity, which they derive from the spinal cord, and are relaxed, soft, and flabby. As the interrupted sensory fibres can no longer convey impressions to the brain, we might naturally look for an anæsthesia, a paralysis of sensation, in the parts to which they are distributed, as complete as is the loss of function in the muscles. Such, however, is not the fact. Long ago cases were observed in which, although sensitive nerves were divided, the region of their distribution retained more or less sensation, or seemed to recover it so quickly that an explanation was sought in a supposed rapid reunion of the cut fibres. Recent investigations, moreover, show that in a large number of cases where there is complete interruption of continuity in a mixed nerve the region to which its sensitive fibres are distributed retains, or rapidly regains, a certain amount of sensation, and that absolute anæsthesia is confined to a comparatively small area, while around this area there is a zone in which the sensations of pain, touch, and heat are retained, though in a degree far below the normal condition; in short, that there is not an accurate correspondence between the area of anæsthesia consequent upon cutting a sensitive nerve and the recognized anatomical distribution of its fibres. We find the explanation of this partly in the abnormal distribution of nerves, but principally in the fact of the frequent anastomoses of sensitive nerves, especially toward their peripheral distribution, thus securing for the parts to which the cut nerve is distributed a limited supply of sensitive fibres from neighboring nerves which have joined the trunk below the point of section. This seems proved not only by direct anatomical investigation, but also from the fact that the peripheral portion of the divided nerve may be sensitive upon pressure, and that the microscope shows normal fibres in it after a time has elapsed sufficiently long to allow all the divided fibres to degenerate, in accordance with the Wallerian law. Some of the sensation apparently retained in parts the sensitive nerve of which has been divided may be due to the excitation of the nerves in the adjacent uninjured parts, caused by the vibration or jar propagated to them by the mechanical means used to test sensation, as tapping, rubbing, stroking, etc.3 It is to be observed that this retained sensation after the division of nerves exists in different degrees in different regions of the body; thus it is greatest in the hands, least in the face.
3 Létiévant, Traité des Sections nerveuses.
As the vaso-motor and trophic nerve-fibres run in the trunks of the cerebro-spinal nerves, destructive lesions of these trunks cut off the influence of the centres with which those fibres are connected, and hence they are followed by changes in the circulation, calorification, and nutrition of the parts to which they are distributed. Thus, the loss of the vaso-motor influence is at first shown in the dilation of the vessels and the unvarying warmth and4 congestion of the part.5 This gives way in time to coldness, due to sluggish circulation and diminished nutritive activity. Marked trophic changes occur in the paralyzed muscles. They atrophy, their fibres becoming smaller and losing the striations, while the interstitial areolar tissues proliferates, and finally contracts cicatricially. The skin is sometimes affected in its nutrition, becoming rough and scaly. Other trophic changes of the skin resembling those produced by irritation of a nerve are very rarely seen, and they may probably be referred to irritation of fibres with which the part is supplied from neighboring trunks.
4 A remarkable exception is seen, however, in the effect of gradual pressure experimentally applied to nerve-trunks until there is complete interruption of sensation and motion, in which case the temperature invariably falls.
5 In a case of gunshot wound that came under the writer's care in 1862, the leg and foot, which were paralyzed from lesion of the popliteal nerve, remained warm and natural in color during repeated malarial chills, which caused coldness and pallor of the rest of the body.
Anatomical Changes in the Divided Nerve and Muscles.—The peripheral portion of a divided nerve separated from its nutritive centres degenerates and loses its characteristic appearance, looking to the naked eye like a grayish cord, and being shrunken to one-fourth of its natural size. The changes which take place in the degeneration of the nerve-fibres, and which proceed from the point of lesion toward the periphery, are, first, an alteration of the white substance of Schwann, which breaks into fragments, these melting into drops of myeline, and finally becoming reduced to a granular mass. The central axis at a later period likewise breaks up, and is lost in the granular contents of the sheath of Schwann. Meanwhile, absorption of the débris of the fibres goes on, until, finally, there remains but the empty and collapsed sheath of Schwann with its nuclei, the whole presenting a fibrous appearance. When this has taken place the degenerated motor nerve-fibres can no longer be excited, and no stimulation applied to them can cause the muscles to contract. At the same time, the muscles atrophy and undergo degenerative changes in their tissue. The fibres become smaller and their transverse striæ indistinct, with the appearance of fatty degeneration, and finally there is proliferation of the interstitial cellular tissue. They do not, however, lose their contractility, and upon a mechanical stimulus being applied directly to them they contract in a degree that is even exaggerated, but with a slowness that is abnormal. If, now, we apply the stimulus of electricity to the muscles themselves, we encounter phenomena of the greatest interest and importance. The application of the faradic current, however strong, elicits no contraction; there is loss of faradic excitability. But if the galvanic current be applied the muscles contract, and that, too, in reply to a current too weak to excite healthy muscles to action; there is increased galvanic excitability. The kind of contraction thus induced is peculiar, differing from that ordinarily seen in muscles. Instead of its being short, and immediately followed by relaxation, as when we make or break the galvanic current in healthy muscles, it is sluggish, long-drawn out, and almost peristaltic in appearance. This is characteristic of degenerated muscles, and is the degenerative reaction. But there is also a change in the manner in which the degenerated muscles reply to the two poles of the galvanic current. Instead of the strongest contraction being elicited, as in the normal condition, by the application of the negative pole to the muscle (C. C. C., cathode closing contraction), an equally strong or stronger is obtained by the application of the positive pole (A. C. C., anode closing contraction), while the contraction normally caused on opening the circuit by removal of the positive pole (A. O. C., anode opening contraction) becomes weaker and weaker, until it is at last exceeded by the contraction upon opening the current by the removal of the negative pole (C. O. C., cathode opening contractions). In short, the formula for the reply of the healthy muscles to galvanic excitation is reversed; there is a qualitative galvanic change in the paralyzed and degenerated muscles.
If no regeneration of the nerve takes place, the reaction of the muscles to the galvanic current is finally lost, and they exhibit those rigid contractions which probably result from a sclerotic condition of the intramuscular areolar tissue.
After complete destruction of the fibres of a nerve at some point of its course, even when a considerable length of it is involved, and after the consequent degeneration of the peripheral portion has taken place, we have, with lapse of time, restoration of its function, consequent upon its regeneration and the re-establishment of its continuity. The histological changes by which the degenerated fibres are restored and the divided ends reunited have not been made out with such certainty as to preclude difference of opinion as to the details. But the process in general seems to be a proliferation of the nuclei in the sheath of Schwann, with increase of the protoplasm which surrounds them, filling the sheath of Schwann with the material from which the new fibre originates. In this mass within the sheath is formed first the central axis of the new fibre, which is later surrounded by the white substance of Schwann. With the regeneration of the nerve-fibres the functions of the nerve return, but in the order of sensation first, and afterward the power of transmitting the volitional impulse to the muscles. Even after regeneration has so far advanced that the muscles may be made to contract by an exercise of the will, the newly-formed fibres fail to respond to other stimuli; thus, the faradic current applied to the nerve does not cause the muscles to contract; the stimulation is not transmitted along the imperfectly restored fibres.
It may be here remarked that after regeneration has restored the functions of a divided nerve the muscles to which it is distributed may still exhibit for a time the degenerative reaction in consequence of unrepaired changes in themselves. In the end we may look for complete restoration in both nerve and muscles.
The time required for the regeneration and reunion of a divided nerve depends somewhat upon the manner in which the destruction has been caused. Thus, a nerve which has been divided by a clean cut, and where the cut ends remain in apposition or close proximity, unites much more readily than one in which bruising, tearing, or pressure has destroyed an appreciable length of its fibres or the divided ends have been thrust apart.
In complete division of a nerve we must not look for regeneration and restoration of its functions, even in favorable circumstances, before the lapse of several months, although cases have been recorded where the process has been much more rapid.
Injuries of mixed nerves, with incomplete destruction of the fibres, give rise to many and varied symptoms, some of which are the direct result of the injury—many others of subsequent changes of an inflammatory character (neuritis) in the nerves or in the parts to which they are distributed. Pain is one of the most prominent symptoms immediately resulting from nerve-injury, although as a rule it soon subsides. There is sometimes merely numbness or tingling, or there may be no disturbance of sensation at the moment of injury. Rarely is spasm of muscles an immediate effect. Generally, motion is at first very much impaired, but if the injury is not grave enough to cause a lasting paralysis, the muscles may rapidly regain their activity. In observing the effects of injuries of mixed nerves one remarkable fact strikes us: it is the very much greater liability of the motor fibres to suffer loss or impairment of function. Thus, it is common to see sensation but little or only transiently affected by injuries which cause marked paralysis of muscles. So in the progress of recovery the sensory disturbances usually disappear long before restoration of the motor function; indeed, sensation may be entirely restored while the muscular paralysis remains permanent. Direct experimental lesions of the mixed nerve-trunks of animals give the same result.6 For this immunity of the sensitive nerve-fibres no explanation can be given other than an assumed difference in their inherent endowments.
6 Luderitz, Zeitschrift für klin. Med., 1881.
According to the amount of damage the nerve has sustained will there remain after the immediate effects of the injury have passed off more or less of the symptoms already described as due to loss of conductivity in the fibres—viz. paralysis of motion, and anæsthesia. Sometimes the impairment of conductivity in the sensitive fibres shows itself by an appreciable time required for the reception of impressions transmitted through them, giving rise to the remarkable phenomenon of delayed sensation. Degeneration of the nerve peripherally from the point of lesion, and consequently of the muscles, will likewise take place in a greater or less degree, according to the amount of the injury and the subsequent morbid changes, and give rise to the degenerative reaction which has been already described. We will not, however, always encounter the degenerative reaction in the typical form which presents itself after the complete division of nerves. Many variations from it have been observed; as, for instance, Erb's middle form of degenerative reaction, in which the nerve does not lose the power of replying to the faradic or galvanic current, but the muscles show both the loss of the faradic with increased galvanic excitability, with also the qualitative change in regard to the poles of the galvanic current. Such irregularities may be explained by the supposition of an unequal condition of degeneration in the nerve and the muscles. A rare modification has been recorded which has once come under the writer's observation, in which the muscles reply with the sluggish contraction characteristic of the degenerative reaction to the application of the faradic current.
A highly important class of symptoms arise later in injuries of nerves, due not so much to a loss as to an exaggeration or perversion of their functions: they are the result of molecular changes in the nerves, giving rise to the condition called irritation. Irritation of motor nerves shows itself in muscular spasm, or contractions of a tonic or clonic character, or in tremor. If the sensitive fibres are irritated by an injury or the subsequent changes in the nerve resulting from it, we may have hyperæsthesia of the skin, in which, although the sense of touch may be blunted, the common sensation is exaggerated, it may be, to such a degree that the slightest contact with the affected part gives rise to pain or to an indescribable sensation of uneasiness almost emotional in its character—something of the nature of the sensation of the teeth being on edge. There may be hyperæsthesia of the muscles, shown by a sensitiveness upon deep pressure, in which the skin has no part. Pain, spontaneous in its character, is a very constant result of nerve-irritation, whether caused by gross mechanical interference or by the subtler processes of inflammation in the nerve-tissue. It is generally felt in the distribution of the branches of the nerve peripheral to the point of lesion, although it is occasionally located at the seat of the injury. Neuralgias are a common result of the irritation of nerves from injuries.
Causalgia, a burning pain, differing from neuralgia, and sometimes of extreme severity, is very frequent after injuries of nerves, especially in parts where the skin has undergone certain trophic changes (glossy skin). A number of abnormal sensations (paræsthesiæ) result from the irritation of sensitive fibres, and are common after nerve injuries. Among these we may mention a sensation of heat (not the burning pain of causalgia) in the region of the distribution of the nerve, which does not coincide with the actual temperature of the part; it occurs not unfrequently after injury to a nerve-trunk, and may be of value in diagnosis.
The effect of irritative lesions of mixed nerves upon nutrition is very marked, and sometimes gives rise to grave complications and disastrous results. Any or all of the tissues of the part to which the injured nerve is distributed may be the seat of morbid nutritive changes.
In the skin we may have herpetic or eczematous eruptions or ulcerations. It may become atrophied, thin, shining, and, as it were, stretched tightly over the parts it covers, its low nutrition showing itself in the readiness with which it ulcerates from trifling injuries. This condition, called glossy skin, usually appears about the hands or feet, and is very frequently associated with causalgia. The hair may drop off, or, as has been occasionally seen, be increased in amount and coarsened, and the nails become thickened, crumpled, and distorted.
The subcutaneous cellulo-adipose tissue sometimes becomes œdematous, sometimes atrophies, and rarely has been known to become hypertrophied. The bones and joints, finally, may, under the influence of nerve-irritation, undergo nutritive changes, terminating in various deformities.
With regard to the trophic changes, as well as to the pain and paræsthesiæ resulting from nerve-injury, we must bear in mind that they may be attributed not only to the direct irritation of trophic and sensitive fibres in the injured nerve, but also, in part, to influences reflected from abnormally excited nutritive centres in the spinal cord, and to the spread of the sensitive irritation conveyed to the brain by the injured fibres to neighboring sensitive centres, thus multiplying and exaggerating the effect, causing, as it were, sensitive echoes and reverberations. Indeed, the variety of the symptoms resulting from apparently similar nerve lesions would seem to point to the introduction of other factors in their causation than the simple injuries of the nerve-fibres themselves.
DIAGNOSIS OF NERVE INJURIES.—Although in the great majority of cases the circumstances attending nerve injuries render their diagnosis a matter of little difficulty, it is yet important to keep in mind those symptoms which distinguish them from lesions or diseases of the brain and spinal cord, inasmuch as in cases of multiple lesion, injuries to the spinal column, or where the history of the case is imperfect, it may be difficult to determine to which part of the nervous system, peripheral or central, some of the gravest resulting troubles are due. Paralysis, spasm, anæsthesia, atrophy, etc. may be of central or spinal as well as peripheral origin, and an intelligent prognosis and rational treatment alike demand that we should distinguish between them. Moreover, many diseased conditions of the peripheral nerves of whose pathology we are ignorant, and in which localizing symptoms—i.e. those indicating the exact point at which the nerve is implicated—are wanting, can only be distinguished as peripheral affections by the occurrence of symptoms which we recognize as identical with those arising from injuries of nerves, in which definite histological changes are known to occur. Indeed, cases of disease of the nervous system are not infrequent in which a careful study of their symptomatology leads to a difference of opinion in the minds of the best observers as to whether their seat is central or peripheral. We will notice here some of the prominent symptoms resulting from nerve injuries which may be useful in distinguishing peripheral from central lesions, although in many cases it is only by the careful consideration of all symptoms and the impartial weighing of all attending circumstances that a probable conclusion can be arrived at.
The rapid loss of muscular tone and the early atrophy of the muscles is a mark of paralysis from nerve-injury which distinguishes it from cerebral paralysis, even when the latter occupies circumscribed areas, as is sometimes the case in cortical brain lesion. In spinal paralysis also the muscles retain their tone and volume (the latter being slightly diminished by disuse), except in extensive destruction of gray matter, when all tonicity is lost, and in lesions of the anterior horns of gray matter (poliomyelitis), when there is loss of muscular tone and marked atrophy. The first of these spinal affections may be distinguished by the profound anæsthesia and by the paralysis being bilateral—by the implication of bladder and rectum and the tendency to the formation of bed-sores; such symptoms being only possible from nerve-injury when the cauda equina is involved. In poliomyelitis the complete integrity of sensation—which is almost always interfered with at some period after nerve-injury—and the history of previous constitutional disturbance will aid us in recognizing the diseased condition. While the reflexes are wanting in peripheral, they are, as a rule, retained, and often exaggerated, in cerebral and spinal paralysis; the exceptions being in the two lesions of the cord above mentioned, in which the reflex arc is of course destroyed by the implication of the gray matter. Loss or alteration of sensation, where it occurs from nerve-injury, generally shows itself in the distribution of the nerve, while the sensitive disturbances from disease or injury of the brain or spinal cord are less strictly confined to special nerve territories. The trophic disturbances arising from nerve-irritation are distinctively characteristic of nerve-injury.
But it is in the behavior of the nerves and muscles to electricity that we find some of the strongest points on which to base a diagnosis of nerve-injury, and, although not always conclusive as to the seat of lesion, it enables us to reduce within very narrow limits the field for discrimination. The degenerative reaction which we have seen takes place in muscles the continuity of whose nerves have been destroyed, or in which degenerative changes have taken place in consequence of injury to their nerves, is never found in muscles paralyzed from the brain. In spinal paralysis resulting from transverse myelitis the electrical excitability of the nerves and muscles may be increased or diminished, but there is no degenerative reaction. In progressive muscular atrophy a careful electrical examination may discover the degenerative reaction in the affected muscles; but it is too obscure, and there are besides too many characteristic symptoms in that disease, to allow of a practical difficulty in diagnosis from its presence. In poliomyelitis anterior (infantile paralysis and the kindred affection in the adult) we have, it is true, the quantitative, qualitative changes of degenerative reaction, such as are seen after nerve-injury, and in such cases its presence is not conclusive of peripheral lesion. Here we may be assisted by remembering that while in poliomyelitis sensation is intact, in nerve-injury it is almost always affected in a greater or less degree, although it may have been recognizable but for a short time. In lead paralysis we also have the degenerative reaction, but whether the seat of lesion in that affection is central or peripheral is an undecided question.
TREATMENT OF NERVE-INJURIES.—The therapeutics of nerve-injuries belong largely to surgery. When there is complete division of a nerve the ends should be united by suture at the time of injury. When this has not been done, and after the lapse of time no return of function is observed, the ends of the nerve should be sought for, refreshed with the knife, and brought together by suture. There is the more hope that such a procedure will be successful as we know that after a time the fibres of the peripheral portion of the nerve may be regenerated, even when there has been no reunion, and thus be in a condition to render the operation successful. It is a matter for consideration whether in injuries in which a certain portion of the nerve, not too great in extent, has been crushed or otherwise obviously destroyed, it would not be best to excise the destroyed portion and bring the ends together. Whether the use of electricity, the galvanic current, hastens the regeneration and restitution of the injured nerves cannot be affirmed with certainty, although in practice this has seemed to us to be the case, and the known catalytic action of the current gives us a possible explanation of such beneficial effects. But, however this may be, it is certain that with the first symptoms of returning function in the nerves and muscles the use of electricity obviously accelerates the improvement. And, again, in the treatment of the results of nerve-injury, such as paralysis, anæsthesia, pain, it is in the careful and very patient use of the electric currents, both faradic and galvanic, that most confidence is to be placed; the galvanic being generally most applicable and giving the better results. The symptoms of nerve-irritation are amongst those most difficult to treat successfully. Counter-irritation, heat, cold, electricity, may all be tried in vain, and as a last resource against pain, ulceration, and perverted nutrition we may be obliged to resort to nerve-stretching, or neurotomy. Under the head of Neuritis much must be said of treatment applicable to the inflammation, acute and chronic, resulting from nerve-injuries.
INFLAMMATION OF NERVES.
Neuritis.
Although inflammation of the nerves has been for a long time a recognized disease, its frequency and the extent and importance of its results have been appreciated only within a comparatively short time. The observations upon neuritis were formerly almost exclusively confined to acute cases, the results of traumatic lesions or the invasion of neighboring disease, while the more obscure forms occurring from cold, toxic substances in the circulation, constitutional disease, etc., or those apparently of spontaneous origin, escaped attention, or were classed according to their symptoms simply as neurosis, functional disease of the nerves, or affections of the spinal cord. Hence the classic picture of neuritis is made to resemble exclusively the acute inflammation of other tissues, and tends to blind as to the subtler but not less important morbid processes in the nerves which at present we must classify as inflammation, though wanting, it may be, in some of the striking features seen in connection with inflammatory processes elsewhere. In short, we must not look for heat, redness, pain, and swelling as absolutely necessary to a neuritis.
Entering into the structure of the peripheral nerves we have the true nervous constituent, the fibres, and the non-nervous constituent, the peri- and endoneurium, in which are found the blood-vessels and lymph-channels. Though intimately combined, these tissues, absolutely distinct structurally and functionally, may be separately invaded by disease; and although it may not be practicable nor essential in every case to decide if we have to do with a parenchymatous or interstitial (peri-) neuritis, it is necessary to keep in mind how much the picture of disease may be modified according as one or the other of the constituents of the nerve are separately or predominantly involved. Thus, a different group of symptoms will be seen when the vascular peri- and endoneurium is the seat of inflammation from that which appears when the non-vascular nerve-fibres are themselves primarily attacked and succumb to the inflammatory process with simple degeneration of their tissue. Furthermore, it is not too speculative to consider that the different kinds of nerve-fibres may be liable separately or in different degrees to morbid conditions, so that when mixed nerves are the seat of neuritis, motor, sensitive, or trophic symptoms may have a different prominence in different cases in proportion as one or other kind of fibres is most affected.
ETIOLOGY.—Traumatic and mechanical injuries of nerves are the most common and best understood causes of neuritis. Not only may it be occasioned by wounds, blows, compression, and other insults to the nerves themselves, but jolting and concussion of the body, and even sudden and severe muscular exertion, have been recorded as giving rise to it. We readily understand how neuritis is caused by the nerves becoming involved in an inflammation extending to them from adjacent parts, although the nerves in many instances show a remarkable resistance to surrounding disease. Less easily understood but undoubted causes of neuritis are to be found in the influence of cold, especially when the body is subjected to it after violent exertion. Although the causal connection is unexplained, we find neuritis a frequent sequel of acute diseases, as typhoid fever, diphtheria, smallpox, etc. In the course of many chronic constitutional affections, as syphilis, gout, elephantiasis græcorum, we encounter neuritis so frequently as to make us look for its cause in these diseases. Finally, neuritis may develop apparently spontaneously in one or many nerves.
MORBID ANATOMY.—The macroscopic appearance of nerves affected by neuritis is very varied, according as the disease is more interstitial or parenchymatous, acute or chronic. Sometimes the nerve is swollen, red, or livid, the blood-vessels distended, with here and there points of hemorrhage, the glistening white of the fibres being changed to a dull gray. Sometimes the nerves are reduced to gray shrunken cords. When the perineurium has been the principal seat of the inflammation we may have swellings at intervals along the course of the nerve (neuritis nodosa, perineuritis nodosa acuta) or, as in chronic neuritis, the trunk of the nerve may be hard and thickened from proliferation of the connective tissue, sclerosis of the nerve. The nerve does not always present the appearance of continuous inflammation, but the evidence of neuritis may be seen at points along its course which are separated by sound tissue. These points of predilection are usually exposed positions of the nerve or near joints. Often the nerve appears to the naked eye normal, and the characteristic changes of neuritis are only revealed by the microscope. The microscopical changes in neuritis may extend to all of the constituents of the nerve, and present the ordinary picture of acute inflammation, hyperæmia, exudation, accumulation of white corpuscles in the tissues, and even the formation of pus, the nerve-fibres exhibiting in various degrees the destruction of the white substance of Schwann and the axis-cylinder. Or, as in chronic neuritis, the alterations may consist in the more gradual proliferation of the peri- and endoneurium, which, contracting, renders the nerve dense and hard and destroys the nerve-fibres by compression. In acute as well as in chronic neuritis the perineurium may be exclusively affected, the fibres remaining normal (Curschman and Eisenlohr). The nerve-fibres themselves may be the primary and almost exclusive seat of the neuritis, exhibiting more or less complete destruction of all their constituent parts, except the sheath of Schwann, without hyperæmia and with little or no alteration of the interstitial tissue. Sometimes the fibres are affected at intervals, the degeneration occupying a segment between two of Ranvier's nodes, leaving the fibre above and below normal (nèvrite segmentaire peri-axile, Gombault). All of these lesions of the nerve-fibres may be recovered from by a process of regeneration, the fibres showing a remarkable tendency to recover their normal structure and function.
SYMPTOMS OF NEURITIS.—When a mixed nerve is the seat of an acute neuritis, with hyperæmia of its blood-vessels, it becomes swollen by inflammatory exudation, and can be felt as a hard cord amongst the surrounding tissues. It is not only highly sensitive to direct pressure, but muscular exertion, or even passive movement of the part, excites pain. Spontaneous pain is one of the most prominent symptoms, and is sometimes so severe and continuous as to destroy the self-control of the patient, and demand the employment of every agent we possess for benumbing sensibility and quieting the excited system. At first there may be hyperæsthesia of the skin in the region of the distribution of the nerve, but a much more constant and significant symptom is cutaneous anæsthesia, which generally makes its appearance early in the course of the disease. The degree and extent of the anæsthesia varies very much in different cases, but is seldom total, except over small areas, even when the inflammation has seriously damaged the nerve-fibres. This is explained by the sensibility supplied to the part by neighboring nerves, as already described in treating of traumatic nerve-injuries. Very characteristic of acute neuritis are various abnormal sensations (paræsthesiæ) which are developed in a greater or less degree during the progress of the disease, and are described by the patients as numbness, tingling, pins and needles, burning, etc. In a case of acute neuritis of the ulnar nerve seen by the writer the patient was much annoyed by a persistent sensation of coldness in the little and ring fingers, which caused him to keep them heavily wrapped up even in the warm weather of summer. When motor symptoms make their appearance they begin with paresis of the muscles, which may increase rapidly to paralysis. As this is the result of destructive changes, more or less complete, in the motor nerve-fibres, we will have, as would be expected, accompanying the paralysis the symptoms already detailed in the consideration of nerve-injuries with destruction of continuity—namely, absence of muscular tone, loss of skin and tendon reflexes, increased mechanical excitability, atrophy of muscles, and the different forms of degenerative reaction, with loss of faradic contractility. When spasm or tremor has been observed in acute neuritis of mixed nerves, it is a matter of doubt whether it is not to be explained by reflex action of the cord excited by irritated centripetal fibres. Various trophic symptoms may show themselves, as herpes zoster or acute œdema. Erythematous streaks and patches are sometimes observed upon the skin along the course of the inflamed nerve-trunks. In chronic neuritis, into which acute neuritis generally subsides or which arises spontaneously, the symptoms above described are very much modified; indeed, cases occur which exist for a long time almost without symptoms. While the affected nerve may be hard and thickened by proliferation of its connective tissue, pain, spontaneous or elicited by pressure, is not of the aggravated character present in acute neuritis, and may be quite a subordinate symptom. It has more of a rheumatic character, is less distinctly localized, more paroxysmal, and has a greater tendency to radiate to other nerves. It is probable that many ill-defined, so-called rheumatic pains which are so frequently complained of are the result of obscure chronic neuritis. Anæsthesia and various paræsthesiæ are often more prominent symptoms than pain. Sometimes there is a hyperæsthesic condition of the skin, in which touching or stroking the affected part causes a peculiarly disagreeable nervous thrill, from which the patient shrinks, but which, however, is not described as pain.
The motor symptoms in chronic neuritis of mixed nerves often remain for a remarkably long time in abeyance or may be altogether wanting. They may appear as tremor, spasm, or contraction, these, however, being probably reflex phenomena. Most commonly there is paresis, which may deepen into paralysis with atrophy of muscles and degenerative reaction. The trophic changes dependent on chronic neuritis are frequently very prominent and important. The skin sometimes becomes rough and scaly, sometimes atrophied, smooth, and shining (glossy skin). Œdema of the subcutaneous cellular tissue is often seen, for example, on the dorsum of the hand, where it may be very marked. The hair of the affected part shows sometimes increased growth, sometimes it falls off. The nails may become thickened, ridged, and distorted. Deformity of joints with enlargement of the ends of the bones is not infrequently met with as the result of chronic neuritis. In short, we may meet with all of those trophic changes which have been described as arising from nerve-irritation, and which occur in chronic neuritis as the result of compression of nerve-fibres by the contraction of the proliferated connective tissue in the nerve-trunk.
The symptom-complex varies greatly in neuritis, so that there is hardly a symptom which may not be greatly modified or even wanting in some cases—a fact, which, as we have already said, may be explained by the morbid process fixing itself exclusively or in different degrees upon one or other of the component parts of the nerve-trunk, or, it may be, upon fibres of different functional endowment. Thus pain, usually one of the most prominent symptoms of neuritis, may be quite subordinate, or even absent, in cases of neuritis acute in invasion and progress. In a case of neuritis of the ulnar nerve seen by the writer, beginning suddenly with numbness and paresis, and rapidly developing paralysis, atrophy of muscles, loss of faradic contractility, with degenerative reaction, there was no pain during the disease, which ended in recovery.7 On the other hand, in mixed nerves the sensitive fibres may be long affected, giving rise to pain and various paræsthesiæ before the motor fibres are implicated, or these last may escape altogether.
7 “Two Cases of Neuritis of the Ulnar Nerve,” Maryland Medical Journal, Sept., 1881.
The swollen condition of the nerve, so characteristic in many cases of neuritis where the perineurium is the seat of a hyperæmia, is wanting in cases where the stress of the attack is upon the nerve-fibres themselves. Again, the trophic changes induced in the tissues by a neuritis may predominate greatly over the sensitive or motor alterations. Thus, in the majority of cases in which herpes zoster occurs it is without pain or paræsthesia. Indeed, in chronic neuritis the symptoms show such variations in different cases that it is difficult to give a general picture of the disease sufficiently comprehensive and at the same time distinctive. The prognosis in acute neuritis is generally favorable, although it must depend in a great measure upon the persistence of the cause producing it. Thus, if it has been excited by the inflammation of neighboring organs it cannot be expected to disappear while these continue in their diseased condition. In other cases the symptoms may subside with comparative rapidity; and so great is the capacity of the nerve-fibres for regeneration that recovery may be complete and nothing remain to indicate the previous inflammation. The nerve, however, that has once suffered from neuritis shows for a long time a tendency to take on an inflammatory action from slight exciting causes. If there has resulted an atrophy of muscles, we must expect some time to elapse before they recover their functional activity and normal electric reaction.
Acute neuritis most frequently passes into the chronic form, and it may then drag on indefinitely, stubbornly resisting treatment and giving rise to permanent derangement of sensibility, loss of muscular power, or perverted nutrition. Neuritis shows a tendency to spread along the affected nerve centripetally, sometimes reaching the spinal cord, and, as it has appeared in some cases, even the brain, causing tetanus or epilepsy.
Reflex paralyses, which at one time were believed to be the not infrequent result of nerve-irritation and inflammation, affecting from a distance the functions of the spinal cord, have been shown to be the effect of an extension of the lesion of the inflamed nerve to the cord, causing organic disease. Instances of the extension of a neuritis to distant nerves, as those of an opposite extremity, without the implication of the spinal cord (neuritis sympathica), are most probably cases of multiple neuritis, to be considered farther on.
The DIAGNOSIS of cases of traumatic neuritis can scarcely present a difficulty. Acute neuritis with spontaneous pain, swelling, and tenderness of the nerve, presents distinctive features hardly to be confounded with any other affection, although thrombosis of certain veins, as the saphenous, may present some of its symptoms. To distinguish chronic neuritis or the cases wanting those obvious symptoms just indicated (many cases of sciatica) from neuralgia is a more difficult task. The following distinctive points may be noted: In neuritis the persistent and continuous character of the pain helps us to distinguish it from the more paroxysmal exacerbations of neuralgia, and its tendency, often seen, to spread centripetally spontaneously or when pressure is made on the nerve, may be also considered as characteristic of neuritis. Cutaneous anæsthesia, paresis, and atrophy of muscles are distinctive in any case of a neuritis rather than a neuralgia. Herpes zoster and other trophic changes speak strongly for a neuritis.
In the TREATMENT of neuritis the first indication is to get rid, as far as possible, of such conditions as may cause or keep up the inflammation, as, for instance, the proper treatment of wounds, the removal of foreign bodies, the adjustment of fractures, the reduction of dislocations, the extirpation of tumors, etc. Absolute repose of the affected part in the position of greatest relaxation and rest is to be scrupulously enforced. In acute neuritis local abstraction of blood by leeches and cups in the beginning of the affection is of the greatest advantage and should be freely employed. The application of heat along the course of the inflamed nerve has appeared to us preferable to the use of ice, although this also may be employed with excellent effect. The agonizing pain must be relieved by narcotics, and the hypodermic injection of morphia is the most efficient mode of exhibition. Salicylic acid or salicylate of sodium in large doses contributes to control the pain. Iodide of potassium in large doses appears to act beneficially, even in cases with no syphilitic complications. In subacute or chronic neuritis local bloodletting is not as imperatively demanded as in the acute form, although it is sometimes useful. Here counter-irritation in its various forms and degrees, even to the actual cautery, is to be recommended. An excellent counter-irritation is produced by the application of the faradic current with the metallic brush. It appears from general experience that the counter-irritation has the best effect when applied at a little distance from the inflamed nerve, and not directly over its course. In the galvanic current we possess one of the very best means not only for relieving the symptoms of chronic neuritis, but for modifying the morbid processes in the nerve and bringing about a restoration to the healthy condition. Its application is best made by placing the anode or positive pole as near as possible to the seat of the disease, while the cathode or negative pole is fixed upon an indifferent spot at a convenient distance. The positive pole may be held stationary or slowly stroked along the nerve. Finally, in protracted cases nerve-stretching may be resorted to with great benefit. It probably owes its good effects to the breaking up of minute adhesions which have formed between the sheath of the nerve and the surrounding tissues, and which act as sources of irritation.
Multiple Neuritis, Multiple Degenerative Neuritis, Polyneuritis.
Cases of this important form of neuritis have been observed and recorded since 1864, but the resemblance of its symptoms to those of certain diseases of the central nervous system (poliomyelitis, Landry's paralysis, etc.) has prevented its general recognition, and it is only within the last few years that its distinctive pathological lesions have been demonstrated and its diagnosis made with considerable certainty. We can hardly overrate the importance of this in view of the great difference in gravity of prognosis between it and other diseases with which it may be confounded.
Multiple neuritis consists in a simultaneous or more or less rapidly succeeding inflammation of several or many usually bilaterally situated nerves, with a greatly preponderating, almost exclusive, lesion of the motor fibres. Commonly the disease attacks the lower extremities and progresses upward, although occasionally it has been seen to begin in the arms. It does not confine itself to the nerves of the extremities and trunk, but often involves the phrenics, causing paralysis of the diaphragm, and frequently invades one or more of the cranial nerves, notably the vagus, thus giving rise to the rapid heart-beat so often seen in the disease. In the cases of multiple neuritis observed the muscles of deglutition have never been paralyzed. The sphincter ani and bladder have likewise escaped. All degrees of acuteness are observed in the course it runs, from the cases terminating rapidly in death to those in which the disease extends over months, slowly involving nerve after nerve, until nearly all of the muscles of the body are paralyzed, when death may result or a more or less complete recovery take place. The invasion of the disease is in most cases sudden, even when its subsequent course is chronic, and is often marked by decided constitutional disturbance, as rigors, fever, delirium, albuminuria, etc. Disturbances of sensation are prominent among the initial symptoms, and are of great importance for the diagnosis of the disease. Severe, spontaneous, paroxysmal pain of a shooting, tearing character has ushered in most of the cases on record, remitting, however, during their progress. Pain is not always present, nevertheless, and cases not infrequently occur which run a painless course. In some cases which have come under the writer's notice spontaneous pain did not occur until some days after the disease was fully declared by other symptoms. More constantly present, and more characteristic of multiple neuritis, are the disturbances of sensation which show themselves in subjective feelings of numbness, tingling, pins and needles, coldness, burning, and other paræsthesiæ, which appear at its outset and continue to be present more or less during its course. Anæsthesia, not of a high degree nor at all coextensive with the paralysis of the muscles—sometimes, indeed, confined to very circumscribed areas—may be said to exist always in multiple neuritis—a fact of great diagnostic value. Hyperæsthesia of the skin is frequently seen. Hyperalgesia and analgesia are sometimes observed. Hyperæsthesia of the muscles is a very marked symptom in almost every case, and shows itself not only upon direct pressure being made, but also in the pain elicited by passive movements of the parts affected. Pressure upon nerve-trunks does not cause pain as invariably as might have been expected from the location of the disease. Delayed sensation has been frequently observed.
Paresis of muscles, often commencing suddenly, is early seen in multiple neuritis, and increases until there is more or less complete paralysis, the most important feature of the disease. The paralyzed muscles present the flabby condition characteristic of muscles deprived of the tonic influence of the spinal cord. Atrophy, which is not commensurate, however, with the paralysis, soon begins, and may go on to an extreme degree. As the paralysis develops the tendon reflexes are lost, and there may be diminution or loss of the skin reflexes also. The paralyzed muscles lose their faradic contractility, and exhibit diminution of electric excitability to the galvanic current, and, finally, the various forms of degenerative reaction. It is remarkable that neither the impairment of sensation nor the paralysis is, as a rule, strictly confined to the areas of distribution of particular nerves, but is diffused over regions of the body. Thus in the limbs the motor and sensory symptoms are most marked at their extremities, gradually diminishing toward the trunk. In some cases multiple neuritis appears to have occasioned the inco-ordinate movements of locomotor ataxy. In the progress of the disease a rigidity and contracted condition of muscles may be developed, occasioning a fixed flexion of some of the joints. Profuse sweating, œdema of the hands and feet, trophic changes in the skin, mark at times the implication of trophic and vaso-motor nerves. Bed-sores do not occur.
The pathological changes in pure cases of multiple neuritis are found in the nerve-trunks, mainly toward their peripheral terminations, and in their muscular branches, the evidences of disease diminishing toward the larger trunks, the nerve-roots being unaffected and the spinal cord showing no lesions. Sometimes the affected nerves present, even to the naked eye, unmistakable proof of acute inflammation. They are reddened by hyperæmia, swollen by exudation, and small extravasations of blood may be seen among their fibres. The microscope shows congestion of the blood-vessels, exudation of the white corpuscles, even to the formation of pus, alteration of the endo- and perineurium; in short, all the evidence of an interstitial inflammation, the nerve-fibres being comparatively little altered, and suffering, as it were, at second hand. In most of the cases, however, the nerves macroscopically present little or nothing giving indication of disease. The microscopic changes, however, are extensive, and pertain almost exclusively to the nerve-fibres themselves. These are altered and degenerated, giving an appearance almost precisely the same as already described in treating of the changes occurring in nerves separated by injury from the centres—Wallerian degeneration.8 There is no hyperæmia, thickening, or change in the endoneurium. So great are these differences in the microscopic appearance of the nerves in different cases of multiple neuritis that objection has been raised to classing the two varieties together, and it has been argued that we cannot with right designate the cases in which hyperæmia and other evidence of a general inflammation are absent as neuritis. It has been, however, argued—apparently, to the writer, with better reason—that the same morbid influence which at one time affects the blood-vessels, causing their congestion and the passage through their walls of the white corpuscles and the exudation of inflammation, may at another time, by a direct and isolated influence upon the nerve-fibres, cause their degeneration; in other words, that there may be a parenchymatous neuritis, which shall affect only the nerve-fibres. The vastly disproportionate implication of the motor fibres would point to the fact of a selective infection in multiple neuritis of certain fibres, as there is a selective infection in poliomyelitis of the motor cells of the anterior horns of the spinal gray matter.
8 Gombault's observations (Arch. de Névrologie, 1880) would seem to show that there is a difference in the lesion of the fibres in neuritis from that in simple Wallerian degeneration, inasmuch as that in the former the first alteration is seen about the nodes of Ranvier, and occurs at points separated from each other by healthy fibre, and also in the more tardy destruction of the axis-cylinder.
ETIOLOGY.—Much in the symptomatology of multiple neuritis, especially of its invasion, strongly urges us to the conclusion that it is a constitutional disease caused by an unknown morbid influence, the stress of which falls upon the nervous system. This view receives strong support from the history of the Japanese kak-ke or Indian beriberi, a disease at times epidemic in those countries, and which has the undoubted symptoms and the characteristic pathological alterations of multiple neuritis. After many acute infectious diseases neuritis of individual nerves is not uncommon, but the distinctive characteristics of multiple neuritis have, so far, been observed almost exclusively after diphtheria, to which it is not infrequently a sequel. It has been observed as the result at least occurring in intimate connection with polyarthritis, and the frequency with which it has occurred in the phthisical is remarkable. There have been not a few cases of multiple neuritis recorded as having been produced by chronic alcohol-poisoning. A well-marked case has come under the writer's observation in which the immediate cause was acute poisoning by arsenious acid, a very large amount having been taken at one dose by mistake. The poison of syphilis has been regarded as standing in a causal relation to multiple neuritis. For the rest, the exciting causes (probably acting in connection with a peculiar condition of the system) have appeared to be exposure to cold, great muscular exertion, direct mechanical injury to the nerves, as the rough jolting of a wagon, or the inflammation of a nerve which has in some unknown way extended to others.
The DIAGNOSIS of multiple neuritis in certain cases presents great difficulty, from the close resemblance of its symptoms to those of poliomyelitis. The prominent symptoms in the muscular system—viz. paralysis, atrophy, the degenerative reaction—are the same in both. It may be remarked, however, that in multiple neuritis the paralysis is more generally diffused over the muscles of the affected limbs, while in poliomyelitis it is more confined to the areas of distribution of particular nerve-branches. Pain is common to the beginning of both diseases, but it generally passes off more quickly and completely in poliomyelitis. The persistent hyperæsthesia of the muscles is wanting in poliomyelitis. But it is in the diminution and alteration of sensation that we have the surest means of distinguishing between the two affections. This symptom seldom or never fails to show itself in multiple neuritis, although its area may be circumscribed and it may be slight in degree, while it certainly makes no part of the symptomatology of poliomyelitis. It has been asserted that the implication of the cranial nerves so often seen in multiple neuritis never occurs in poliomyelitis. When we consider the intimate connection of the anterior horns of the spinal gray matter with the motor nerve-fibres, it appears highly probable that the same morbid influence may invade both simultaneously or in quick succession, thus producing a complex of symptoms rendering a diagnosis very difficult, and probably giving rise to some confusion in the recorded symptoms of multiple neuritis. From Landry's paralysis multiple neuritis is to be distinguished by the impairment of sensibility, the loss of faradic contractility, and absence of the tendon reflex; from progressive muscular atrophy, by the loss of sensibility and the much more obvious degenerative reaction.
The PROGNOSIS of multiple neuritis is in the great majority of cases not grave, so far as life is concerned, even when there is extensive paralysis. Death may occur early in the acute form of the disease or it may take place at the end of chronic cases. When the disease proves fatal, it is from paralysis of the diaphragm and the other muscles of respiration. Where the paralysis and atrophy have been great, showing profound alteration of the nerves, a long time is required for recovery, and more or less paralysis, contracture, or defective sensibility may permanently remain.
The TREATMENT consists, at the outset, in rest and position, the local abstraction of blood (in cases where the nerve-trunk is swollen and tender), and the administration of such drugs as we suppose act favorably upon the inflammation of the nerves. Salicylic acid or salicylate of sodium seem to act beneficially in relieving the severe pains in the outset of the disease. Iodide of potassium, gradually increased until large doses are taken, has, in the experience of the writer, seemed to beneficially modify the course of multiple neuritis. The necessary relief of pain is best obtained by hypodermic injections of morphia, supplemented by heat applied to the affected nerves. To these means may be added rubbing with chloroform and applying to the painful parts cloths dipped in a 5 per cent. solution of carbolic acid. After the acute stage has been passed and in chronic cases, just as soon as we have reason to suppose that the degenerative process in the nerves has come to a standstill, we possess in the use of electricity the means of hastening the regeneration of the nerve-fibres, strengthening the paralyzed muscles, and restoring the sensation. The galvanic current is to be preferred, and it is to be applied to the crippled nerves and muscles—sometimes stable for its electrolytic action, sometimes interrupted to obtain its exciting and stimulating effect. The excitement to nerves and muscles by the use of the faradic current has also its uses in hastening recovery. Protracted treatment and much patience are required to overcome contractions and restore the nerves and muscles, and the effects of the disease may be seen for a long time in the weakness and diminished electric reaction of the muscles.
Anæsthesia of Peripheral Origin.
A prominent and important symptom of the lesion of peripheral nerves is the diminution and loss of cutaneous sensibility. Besides the anæsthesia caused by the affections of the fibres themselves, which has been touched upon in the preceding pages, it may be produced by morbid states of the peripheral end-organs or cutaneous terminations of the nerves. Cold applied to a nerve-trunk may produce alterations which for days after cause numbness and paræsthesia in the surface to which it is distributed, and the application of cold to the surface of the body, as we know from common observation, causes blunting of the cutaneous sensations, especially that of touch. In this way, from exposure to the atmosphere at low temperatures, to cold winds, or by the immersion of the body in cold water, the end-organs of the nerves in the skin are morbidly affected, and anæsthesia results, the so-called rheumatic anæsthesia. Many substances, as acids, notably carbolic acid, alkalies, narcotics, etc., act upon the cutaneous end-organs in a way to destroy their capacity for receiving or transmitting impressions and produce a more or less persistent anæsthesia of the skin. In the anæsthesia so often observed in the hands and forearms of washerwomen we have an example of the action probably of several of these causes, as the frequent plunging of the hands into cold water and the action upon the skin of alkalies and alkaline soaps. The diminution or interruption of the circulation through the skin, as in ischæmia from spasm of the minute arteries due to an affection of the vaso-motor nerves, is also a cause of cutaneous anæsthesia. In lepra anæsthetica (Spedalskhed) the cutaneous anæsthesia is dependent upon a neuritis of the minute branches in the skin. The local anæsthesia met with so often in syphilis, though its pathology is doubtful, is not improbably sometimes caused by an affection of the peripheral nerves (neuritis?) and their end-organs. After many acute diseases, diphtheria, typhoid fever, etc., we have cutaneous anæsthesia in connection with muscular paralysis, the cause of both being a neuritis. The patient is made aware of the loss of sensation by some interference with his usual sensations and movements. If he puts a glass to his lips, the sensation is as if a bit were broken out of the rim; his accustomed manipulations are awkward, because of the want of distinct appreciation of the objects he holds; he fumbles in buttoning his clothes or he stumbles unless looking to his steps. An examination, nevertheless, almost always reveals that the anæsthesia is greater than would have been supposed from the subjective feelings of the patient; indeed, cases occur in which he is not aware of an existing defect of sensation. But a careful examination is not only required to determine the extent, but by it alone can we arrive at a knowledge of the quality of the anæsthesia—viz. whether there is a loss of all of the different kinds of sensation, whether they are affected in an unequal degree, or whether some have entirely escaped. Thus we must test for the acuteness of the simple sense of touch by comparing the sensations elicited by the contact of small surfaces of unequal size, as the point and head of a pin or pencil, observing the appreciation by touch of the patient for different substances, as woollen, silk, linen, cloth, or comparing the sensation of the anæsthesic part with the same part on the opposite healthy side of the body. The sense of locality and space may be examined by placing at the same instant upon the skin of the patient, his eyes being closed, two points (the anæsthesiometer or the points of a compass), and observing his capacity for appreciating the impression as double. As there is an enormous difference of acuteness of the space-sense in the skin of different parts of the body (see textbooks of physiology)—ranging from the tip of the tongue, where the touch of two points separated 1.2 mm. gives a double sensation, to the thigh, where the points must be separated 77 mm. to be felt as two—we must be careful to consider in making the examination the normal space-perception of the region. Care must be taken not to repeat the test too often, as a rapid education of the surface to a more delicate appreciation of the impressions is the result. In certain abnormal conditions from spinal disease we have a condition of polyæsthesia in which the impression of one point is felt as two or more. The sense by which we appreciate the pressure of objects must be tested by placing upon the surface to be examined, in succession, objects of different weight, care being taken to have the area which touches the skin and the temperature the same in each. The parts to be tested must be firmly supported, and all muscular contraction on the part of the patient prevented. The temperature sense is examined by the application of hot and cold water or bodies of different temperature. We sometimes meet with a perversion of this sense in which the application of a cold surface to the skin gives the sensation of warmth, and the contrary. In testing the sense of temperature and the sense of pressure it is not the absolute capacity of appreciating on the part of the patient that we investigate, but the power of discriminating between different degrees of temperature or pressure. The sense of pain must likewise be tested, since morbid conditions occur in which it may be caused more readily than is normal by exciting the cutaneous nerves, and that, too, in parts which have in a great measure or quite lost the sense of touch; or, on the other hand, touch may be retained, while irritation of the skin can excite no feeling of pain (analgesia). We have in the faradic current an excellent means of testing the cutaneous sensibility, inasmuch as it excites the skin over the various parts of the body about equally, and it can be employed in very gradually increasing or decreasing strength. Its effects on the affected part must be compared with those produced on the healthy surface of other parts of the patient's body or on healthy individuals.
Frequently accompanying cutaneous anæsthesia, but constituting no part of it, are various paræsthesiæ, as formication, pins and needles, burning, etc. Pain, sometimes of great intensity, is not infrequently connected with it (anæsthesia dolorosa). The paræsthesiæ and pain are the result of irritation in some portion of the conducting tracts, and, together with the trophic changes so often seen in connection with nerve-injuries, they have been already considered under that head.
It is a very important point to make the diagnosis between central and peripheral anæsthesia, but it is often a matter of great difficulty, and sometimes not to be made at all. The history of the case must be carefully considered, and an examination made for symptoms of brain or spinal disease, the existence of nerve lesions, or if there is a history of toxic influences, etc. In peripheral anæsthesia the reflexes which may be normally excited from the affected surface are wanting, in contradistinction to anæsthesia of central origin, in which they are most generally retained or even increased. Concomitant trophic changes speak strongly for a peripheral origin, as do also paralysis and atrophy of muscles. Loss of some of the forms of sensation, with retention of others—i.e. partial paralysis of sensation—indicate a central origin.
The TREATMENT of peripheral anæsthesia must look, in the first place, to removal, if possible, of its cause, and the treatment of diseased conditions, if any exist, of the nerve-trunks, as neuritis, mechanical injuries, etc. Local applications of a stimulating character may be advantageously used upon the anæsthesic parts. By far the most effective stimulant to the diseased nerves is the faradic or galvanic current, and it should be used in the way that will produce the greatest amount of excitation in the cutaneous end-organs. This is best done by applying the faradic current to the dry skin with the metallic brush, or by allowing the cathode of the galvanic current to rest upon it for some time.
The PROGNOSIS in peripheral anæsthesia is in the main favorable, but it must, of course, depend much on the gravity of the lesion causing it, as mechanical injury, pressure, neuritis, cold, etc. Rheumatic anæsthesia, the result of exposure to cold, is in general readily recovered from. Vaso-motor anæsthesia yields in most cases without difficulty to treatment. Washerwoman's anæsthesia and allied cases are intractable, and often resist the patient and well-conducted application of remedies.
As a concrete picture of peripheral anæsthesia we will give a description of anæsthesia of the fifth nerve—the rather that in its consideration we meet with some of the most interesting and important complications occurring in connection with paralysis of sensitive nerves. The fifth nerve may have either of its three branches separately affected, giving rise to anæsthesia limited to the distribution of that branch, or all of its fibres may be simultaneously involved, giving rise to complete anæsthesia of the nerve. In the latter case the lesion of the nerve in all likelihood exists at some point of its course between the apparent origin from the pons and the ganglion of Gasser, which rests upon the apex of the petrous portion of the temporal bone. Beyond this point the nerve divides into its three branches. Amongst the causes of trigeminal anæsthesia are injuries, tumors, syphilitic thickening of the dura mater, neuritis, etc., affecting the nerve within the cranial cavity. In complete anæsthesia of the fifth nerve the parts implicated are the skin of the forehead to the vertex, the nose, the lips, and chin up to the median line, the cheek and temporal region, including the anterior portion of the ear, the conjunctiva, the mucous membrane of the nose, the mucous membrane of the mouth, and partly of the fauces of the same side. The tongue is deprived not only of common sensation on the affected side in its anterior two-thirds, but the sense of taste is also lost over the same region, by reason that the fibres of the chorda tympani, the nerve of taste for this region of the tongue, are derived from the fifth nerve. If the whole thickness of the nerve-trunk is involved, including the small motor root, there is, in connection with the anæsthesia, paralysis of the muscles of mastication on the side affected, which may be distinguished by the want of hardening of the masseter when the jaws are forcibly brought together, and by the thrusting of the chin over to the paralyzed side when the mouth is widely opened, caused by the want of action of the external pterygoid muscle, which allows the condyle on the paralyzed side to remain in the glenoid fossa, while the condyle of the opposite side is pulled forward upon the articular eminence by the sound pterygoid. The face is of a dusky or livid color, and cooler than natural. Ulcers of a stubborn character in the mucous membrane of the cheek may be caused by the patient unconsciously biting the insensitive parts. An inflammation of the conjunctiva is frequently set up, which may extend to the cornea, causing ulceration, perforation, panophthalmitis, and destruction of the eye (ophthalmia neuro-paralytica). This has been regarded by some as caused by trophic changes in the tissues, the direct result of irritation or destruction of trophic fibres connected with the ganglion of Gasser. Experiments made upon animals, however, seem to show that the inflammation of the eye depends upon the irritation caused by the intrusion of foreign bodies, which, owing to the loss of sensation, are not appreciated, and which from loss of reflex action are not removed by winking nor washed away by an increased lachrymal secretion, as in the healthy eye. It may be that although the latter is the true explanation of the origin of the inflammation, nevertheless the tissues may have lost their normal power of resistance to its invasion by reason of nutritive changes consequent upon the lesion of trophic fibres running in the trunk of the nerve. The reflexes ordinarily induced by irritation of the parts in their normal state are lost. Irritation of the conjunctiva causes no winking of the lids nor secretion of tears, and titillation of the nostrils no movements of the muscles of the face nor mucous or lachrymal secretion. The movements of the face are less lively on the affected side, not on account of paralysis of the muscles, but from the loss of that constant play of reflex activity in them which takes place in the normal condition. The loss of the reflexes distinguishes peripheral trigeminal anæsthesia from that of cerebral origin, in which they may still be excited by irritating the anæsthesic surfaces. In trigeminal anæsthesia, which sometimes occurs from the effect of cold upon the surface of the face, the mucous surfaces are not affected.
The SYMPTOMS and DIAGNOSIS of peripheral paralysis having been already given under the heads of Injuries of Nerves and Neuritis, a consideration of the distribution of any motor nerve will enable us to anticipate the distinguishing features of the paralysis dependent upon it. With each the picture will be modified according to the position of the muscles paralyzed and the motor functions destroyed. It now remains to give the symptoms, diagnosis, and treatment of the paralysis of an individual motor nerve, which may serve as an example and paradigm, in the consideration of which points of interest and instruction may be touched upon applicable to all other cases.
Peripheral Paralysis of the Facial Nerve (Bell's Paralysis).
Of all the peripheral paralyses, probably that of the seventh is the one we are most frequently called upon to treat and the symptoms of which are the most complex and interesting. The frequency of its paralysis is due to the length and peculiarity of its course, enclosed as it is in a bony canal which permits no increase of its volume without compression, the run of its terminal branches through parts liable to inflammation and disease (parotid gland), and their final distribution to parts exposed to all vicissitudes of heat and cold and in constant danger of mechanical injury. The complexity and interest of the symptoms of its paralysis depend in a great measure upon the intimate connections it forms at different points of its course with the fibres of other nerves of entirely different functions (acoustic and fifth).
The seventh nerve is liable not only to intercranial compression from tumors, inflammation of the meninges, syphilitic processes, etc., but its long course through the petrous portion of the temporal bone renders it liable to injury from fracture or caries, and its close proximity to the middle ear causes it often to suffer from the diseased conditions of the bony walls or mucous lining membrane of that chamber, its paralysis being not infrequently the result of simple aural catarrh. After the exit of the nerve from the stylo-mastoid foramen it is imbedded in the parotid gland, and sometimes suffers from compression produced by an inflammation or abscess in that organ or by enlarged lymphatic glands in the neighborhood. Surgical operations, so often demanded for disease of the bones or soft parts of the face, may necessitate the lesion of its trunk or branches. The exposed position of this nerve is sometimes the occasion of its injury at the very outset of the life of the individual, when the application of the forceps to the head has been resorted to in delivery. But the most frequent cause of facial paralysis appears to be the exposure of one side of the face directly to cold—as sleeping in a draught of air, sitting at the open window of a railroad coach, etc. Here the causal connection appears evident from the rapidity with which the paralysis usually follows, although cases occur in which an interval of hours or days elapses after the exposure before the paralysis declares itself. Although this is usually designated rheumatic paralysis, there is nothing to connect it with that disease, nor are rheumatics more liable to it than others. Under such circumstances the paralysis is probably brought about by the occurrence of a neuritis of the nerve-trunk, which is compressed by the hyperæmia, and it may be by an inflammatory exudation against the bony walls surrounding it, until not only does it lose the power of conduction, but its fibres undergo the degenerative process. In some cases the neuritis thus excited by exposure to cold attacks the nerve after it has issued from the bony canal, and then the resulting injury to the fibres is much less grave. Although in some cases there are prodromal symptoms, as stiffness or pain in the face, generally the paralysis occurs suddenly, very often being first observed upon awaking. The patient may be first made aware of the paralysis by an inability to drink without the fluid dribbling from the affected side of the mouth or by the overflow of tears from the eye of the same side. When the paralysis is recent and the face in complete repose, there may be little or no deformity to mark the condition of the muscles. When, however, the patient speaks or the slightest emotional or reflex movements of the face are excited, as laughing, frowning, etc., it becomes obvious from the bizarre grimace caused by a one-sided contraction. After the paralysis has existed for some time the contrast of the two sides of the face is marked. The paralyzed side is characterized by a vacancy of expression to which the staring, unwinking eye contributes. From loss of the tonicity of the muscles the angle of the mouth droops, and the expressive furrows and lines about the brow, below the eye, and beside the nose are smoothed out and obliterated. Speech is affected, inasmuch as the paralysis of the lip interferes with the pronunciation of the labials, and all attempts to purse up the mouth, as in whistling, is abortive. The eye not only remains open, the lids motionless, but there is partial eversion of the lower lid (lagophthalmos), and the tears, no longer directed to the punctum (paralysis of Horner's muscle), flow over the cheek. The natural impulse to reflex winking caused by evaporation from the conjunctiva or by the contact of particles of dust is answered by a rolling of the eyeball upward to wipe the cornea beneath the momentarily relaxed and drooping upper lid. Excited respiration causes no movement of the ala of the nose on the affected side, but in deep inspiration, in contrast to the normal elevation of the ala, it is flattened down by the suction of the inrushing current of air. In masticating, the cheek bulges out from want of power in the paralyzed buccinator to press the food inward against the opposing movements of the tongue. In persons who have the rather unusual power of voluntarily moving the ear we may detect the paralysis of the muscles concerned in those movements—a useful point in diagnosis. Moreover, on the sound side of the face the features have not entirely the natural appearance. The angle of the mouth is drawn upward and the naso-labial line more deeply impressed than natural. This results not from excessive contraction, but from the muscles remaining in the position they have taken during contraction, the antagonistic tonic traction from the opposite side, which would have restored them to their normal position, being wanting. This may be in a measure remedied by mechanical appliances which will keep up an elastic pull from the paralyzed side, or by restoring the muscles after contraction to position with the hand. The tongue rests symmetrically in the floor of the mouth, and is thrust out straight, although in appearance it is pushed toward the side paralyzed—a deceptive appearance produced by the asymmetrical position of the mouth. In some cases there is partial paralysis of the velum palati, the half arch on the affected side hanging lowest, and if we cause the patient to make the sound of ah the opposite side of the palate is alone drawn upward. The uvula may also participate in the paralysis, but the explanation of its position, sometimes directed away from, sometimes toward, the side of the paralysis, cannot be given. In proportion to the amount of the paralysis of the soft palate will be the prominence of the symptoms caused by it, such as difficulty in deglutition, a nasal tone in speaking, and the escape of fluids through the nostril in swallowing. The sense of hearing is often affected coincidently with facial paralysis. Thus by reason of their close juxtaposition the same cause may in common affect the acoustic and the facial, causing imperfect hearing, subjective noises, etc. The hearing is frequently affected by diseased conditions of the middle ear, which also cause a facial paralysis. Still another defect of hearing, however, is caused by the paralysis of the facial nerve itself. The stapedius muscle, supplied by a branch of the facial, is the antagonist of the tensor tympani, and when it is paralyzed the over-tense tympanic membrane vibrates more readily to sound-waves, and a condition of uncomfortably exaggerated sensitiveness to sounds is the result (hyperacuisis). The rarely-occurring symptom of dryness of the mouth on the side of the paralysis receives its explanation in the well-known fact of the presence of secretory fibres for the salivary gland in the chorda tympani, which are derived from the facial. We observe sometimes, in connection with facial paralysis, that the patient complains of certain subjective sensations of taste, as sour or metallic, and an examination will in some cases reveal that the sense of taste is lost on the anterior two-thirds of the tongue on the side of the paralysis. The fibres which convey the sense of taste pass centripetally from the tongue in the chorda tympani nerve, join the facial just within the stylo-mastoid foramen, and continue united with it to the geniculate ganglion of the facial, at which point they leave it to pass in the great superficial petrosal to the spheno-palatine ganglion, and thence to the trunk of the fifth nerve. Loss of sensation over the face only occurs in cases where the fifth nerve has been simultaneously affected with the facial, which may occur from exposure to cold.
It is obviously of importance in cases of facial paralysis to determine if they are of central or peripheral origin. The most prominent symptoms which mark a peripheral paralysis are the implication of all the branches of the nerve, the loss of the reflexes, the development of the degenerative reaction, and atrophy of the muscles. In facial paralysis of cerebral origin the frontal and orbital branches are not at all or but slightly affected, leaving the eye with its natural appearance, in contrast to the lagophthalmos, and the open eye which does not close even in sleep. In cerebral paralysis the reflexes are normal and the muscles retain their natural electric reaction. Accompanying brain symptoms assure the diagnosis. In facial paralysis of bulbar origin the electric reactions are diminished, and we have a complex of symptoms made up in a great measure by the implication of neighboring nerves. After the diagnosis of a peripheral facial paralysis has been made, by a careful consideration of the symptoms we may with more or less accuracy determine at which point of the nerve the lesion is situated. If there is paralysis of all the muscles of the face, without alteration of taste or hearing, the electric reaction of nerve and muscles normal, the nerve is affected outside of the stylo-mastoid foramen. This is usually the form of slight rheumatic paralysis. If we discover that the muscles of the external ear are paralyzed, it shows that the point of lesion is just within the stylo-mastoid foramen, where the posterior auricular branch is given off from the facial. If with paralysis of the face there is alteration of the sense of taste, with dryness of the mouth, without interference with hearing, the trunk of the nerve is affected within the Fallopian canal, involving the chorda tympani fibres below the point where the stapedius nerve is given off. If to the above symptoms there is added over-sensitiveness to sounds, hyperacuisis, and there is no paralysis of the palate, we have the nerve affected still higher up, but below the geniculate ganglion. If the geniculate ganglion is involved, there is, in addition to the foregoing, symptoms of paralysis of the palate. If, now, the lesion is above the geniculate ganglion, we will have eliminated the symptom due to implication of the chorda tympani, which leaves the trunk of the facial at the geniculate ganglion, and the sense of taste is unaffected, while there remains paralysis of the face, dryness of the mouth (the secretory fibres run in the trunk of the seventh), hyperacuisis, and paralysis of the palate.
It was in facial paralysis that the first observations upon the degenerative reaction in muscles were made, and it is in that affection that these electric phenomena have been best studied, and give us the clearest indications for prognosis and treatment in peripheral paralysis generally. In rheumatic facial paralysis, the most common form of peripheral facial paralysis, the electric reactions of the paralyzed muscles enable us to classify the cases into three groups, the prognosis and duration of which vary very much. In the first group are the slight forms of facial paralysis. Here the faradic or galvanic current, applied to nerve or muscles, causes an ordinary contraction; the electric reactions are normal. These cases scarcely require treatment, and recover in two or three weeks. In a second group are those cases in which within a short time after the invasion of the paralysis (two weeks) complete degenerative reaction is observed. This degenerative reaction, with the accompanying anatomical changes in nerve and muscle, has already been treated of in this article, and it is sufficient here to say that it is marked by total loss of electric excitability, both faradic and galvanic, in the nerve, loss of faradic and increased galvanic excitability in the paralyzed muscles, with a reversal of the normal reply of the muscles to the different poles of the galvanic battery. These cases constitute the severe form of rheumatic facial paralysis, and the prognosis is grave, recovery takes place only after months, and even after the lapse of years traces of the disease remain in the imperfect action of the muscles. A third group of cases are of a gravity intermediate between these two. In them is present the milder form of degenerative reaction; that is, there is a diminution, but not a total loss, of electric excitability in the nerve for both the galvanic and faradic currents; but in the muscles there is a marked increase of galvanic excitability, with qualitative change—i.e. greater contraction upon application to them of the positive than of the negative pole. These cases may be expected to recover in from four to eight weeks, the muscles still exhibiting the degenerative reaction after voluntary motion has returned. Among the symptoms to be particularly noticed in the progress of the severe forms of facial paralysis are spasmodic twitchings or spasms of the muscles on the affected side of the face, about the angle of the mouth, and around the eye, occurring spontaneously or when voluntary movements are made. Also a state of tonic contraction and rigidity may develop in some of the muscles, causing a permanent elevation of the angle of the mouth, a narrowing of the opening of the eye, or a rigidity of the cheek. These symptoms have been erroneously attributed to the use of electricity in the treatment, but they occur as frequently in cases in which it has not been employed. Traumatic facial paralysis, as from wounds, surgical operations, use of the forceps in delivery, or paralysis from compression of the nerve, as from tumors, syphilitic thickening of the dura mater, etc., do not require a detailed mention here, as such cases come under the head of nerve-injuries, already discussed. Paralysis of both facials (diplegia facialis), in so far as it is caused by peripheral nerve lesion, is an accidental occurrence, and need not be considered as a separate form of facial paralysis. It is often the result of central disease.
The TREATMENT of peripheral facial paralysis must begin with the effort to remove its cause. If syphilis is suspected, mercury and iodide of potassium must be freely used. If the cause is an affection of the middle ear, this must be treated. Wounds or traumatic injuries must receive the necessary surgical attention. In addition, in such cases electricity must be employed in the manner presently to be described. In cases of rheumatic facial paralysis the treatment will vary with their gravity. In the lighter form in which the nerve is affected outside of the Fallopian canal, recovery takes place in a comparatively short time, even without treatment, but is hastened by the use of the faradic or galvanic current daily along the branches of the nerve. In the severe form we must open the treatment by an attempt to combat the condition of inflammation—of inflammatory exudation—which we suppose exists within the Fallopian canal. Local blood-letting by leeching upon the mastoid process may be appropriately used in the very first outset of the paralysis. Iodide of potassium, given persistently in large doses during the earlier period of the disease, appears to act beneficially independently of any syphilitic taint. Electricity is the remedy, however, on which most reliance is to be placed in the treatment of rheumatic facial paralysis, and the manner of its application may be taken as a model of how it should be employed in all cases of peripheral paralysis. The galvanic current, on account of its power of penetrating to the deeper parts and its catalytic action, is to be preferred for the direct electrical treatment of the nerve which should be instituted in recent cases. Its action is best obtained by placing the positive pole behind the ear on the affected side, the cathode behind the opposite ear, and passing a moderate current across the base of the skull (the affected nerve being thus in the course of the current) for one or two minutes. Occasionally the position of the poles may be reversed. Besides this direct application of galvanism to the point of lesion, it is necessary to make a peripheral application of electricity to the branches of the nerve and to the paralyzed muscles. For this we use both the faradic and galvanic currents. The galvanic current is used by applying the positive pole stationary behind the ear, while the negative pole, with an electrode of suitable size, is stroked over each branch of the nerve and applied to each muscle, a current being used sufficiently strong to produce decided contractions. This peripheral application should be made once daily, the time of application being from two to five minutes. The application of the faradic current is made by simply placing one electrode upon an indifferent spot, and moving the other over the face, with a current strong enough to cause contractions if the muscles still respond to it, or if they do not of such strength as the patient can bear without discomfort. Without doubt, one of the beneficial effects of peripheral electrization is the reflex excitement of the facial above the point of lesion through the irritation of the terminations of the fifth nerve in the skin. A certain advantage derived from it is that it maintains the tone of the paralyzed muscles, which in the case of the orbicularis palpebrarum is of great importance in preventing the eversion of the lower lid and the overflow of the tears. As it is impossible during the first days succeeding the paralysis to distinguish severe cases from those of the middle form, it is best to begin the treatment of all cases in the manner above described. The use of strychnia in rheumatic facial paralysis, both internally and by hypodermic injection, may be mentioned on account of the widespread preposession in its favor, and to point out distinctly its utter futility.
Mechanical appliances and manipulation are used with advantage in the treatment of facial paralysis to prevent the paralyzed muscles about the mouth and cheek from being drawn out of place and over-stretched by the action of the sound ones of the opposite side, thus having their tonicity and nutrition impaired.
Contractions and rigidity of muscles receive little benefit from the use of electricity, and must be treated by mechanical procedures, such as stretching, massage, etc.
Neuromata.
The term neuromata was applied to all tumors involving the nerve-trunks at a time when their histological differences had not been studied and they were all supposed to be composed of nerve-tissue; and even yet the name is conveniently retained, because, although differing widely histologically, tumors situated upon the nerves have a very similar clinical history.
Neuromas must be divided into true and false, the true consisting of nerve-tissue, the false, or pseudo-neuromas, being composed of many varieties, having this only in common, that they are seated upon the nerves.
The true neuromas are again subdivided into those in which the nerve-tissue composing them resembles exactly the fibres of the peripheral nerves, showing with the microscope the double-contoured white substance of Schwann surrounding an axis-cylinder, and those in which the tumor is made up of fibres which Virchow has shown to be non-medullated nerve-fibres—i.e. the axis-cylinder without the white substance of Schwann. These two forms have been distinguished by the names myelinic and non-myelinic. The true neuromas are non-malignant, although showing the tendency to recur after extirpation, are of slow growth, and as a rule do not increase to a very great size. The best type of the myelinic neuromas is found in the spherical or spindle-shaped enlargements at the cut ends of nerves, particularly in the stumps of amputated limbs, where they are found oftenest intimately connected with the cicatricial tissue, though sometimes lying free. They consist of true medullated fibres mixed with some fibrous tissue. The fibres composing them are derived partly from splitting up and proliferation of the fibres of the nerve itself, partly are of new formation, the appearances strongly recalling the process of regeneration in nerves. Myelinic neuromas consist of fibres and nuclei so closely resembling in microscopic appearance the fibromas that they have hitherto been confounded with them; and there is a difference among the highest authorities as to the certainty of their diagnosis, and, in consequence, of the frequency of their occurrence. The true neuromas may include in their structure all of the fibres of the nerve-trunk or only a portion of them (partial neuroma)—a fact of importance in their symptomatology. Of the false neuromas, the fibromas are by far the most frequently met with. They appear as knots, more or less hard, upon the course of the nerve-trunk, which they may involve completely or partially. They are often excessively painful to the touch or spontaneously, most of the so-called tubercula dolorosa belonging to the fibro-neuromas. Fibromas sometimes occur along the trunk and branches of a nerve, forming a plexus of knotted cords (plexiform neuroma). Fibro-sarcomas are not an infrequent form of neuroma.
Myxomas often occur upon the peripheral nerves, and are frequently multiple, their points of predilection being the larger trunks, as the sciatic, ulnar, etc. They show their characteristic soft structure, and are usually spindle-shape, assuming a rounder form as they attain a large size. The various forms of sarcoma occasionally form tumors upon the nerves, attacking generally the large trunks. Carcinomatous tumors beginning upon the nerves sometimes occur, but as a rule these growths involve the nerve by extension to it from adjacent parts.
Syphilitic gummata have been found almost exclusively upon the intracranial portion of the cranial nerves.
Gliomas appear to affect only the optic and acoustic nerves. Lepra nervorum (lepra anæsthetica) produces usually a spindle-form thickening upon the nerve-trunks, but sometimes there are more distinct knots, which may be felt beneath the skin, bead-like, along the course of the nerves of the extremities.
Like the true neuromas, the false neuromas, developing from the neurilemma and perineurium, may involve the whole or only a part of the fibres of a nerve, or the nerve-fibres may run at the side of the tumor—different conditions, which may alter materially the effects produced upon the nerve.
Neuromas, both false and true, may occur not only singly, but often in large numbers, many hundreds having been counted upon an individual. Sometimes they are numerous upon a single nerve-trunk and its branches, and again they may appear scattered over nearly all of the nerves of the body, even to the cauda equina and roots of the nerves. According to Erb,9 isolated neuromas are more frequent in females, while multiple neuromas are found almost exclusively in men. Neuromas vary greatly in size, as we might expect from the very great difference of their nature and structure; sometimes no larger than a pea, they may attain the size of a child's head.
9 Ziemssen's Handbuch.
ETIOLOGY.—In cases of multiple neuromata it would seem as if there was a constitutional condition or diathesis as the foundation of the affection. This we may the more readily believe as there appears good evidence to show that the tendency to the formation of these nerve-tumors is sometimes hereditary, and some of them are congenital.
Idiots and cretins have been observed to suffer in undue proportion with multiple neuromas. We find a direct exciting cause of neuromas in mechanical injuries of nerves, wounds, blows, pressure, etc. Thus, as has been already seen, true neuromas occur in the divided ends of the nerves after amputations or otherwise where a nerve-trunk has been divided (cicatricial neuroma). As such neuromas are in some degree the result of inflammation, it is probable that they may sometimes be caused by chronic neuritis.
For a large number of neuromas no cause can be assigned, and we must at present consider them as originating spontaneously.
SYMPTOMS.—The position and connections of neuromas being so different, sometimes simply in contact with the nerve; sometimes situated in the thickness of the nerve-trunk, the fibres being pressed aside and spread out upon the surface of the tumor; sometimes involving in their tissue a part or the whole of the nerve-fibres,—we cannot but expect a very marked difference in their clinical history. Not a few cases occur in which the presence of neuromas, even in large numbers, gives rise to no symptoms during life, and their existence has been revealed only upon a post-mortem examination.
The symptom most common to neuromas, and one to be expected from their mechanical interference with the nerves, is neuralgic pain—sometimes extreme, local or shooting along the course of the nerves, stubborn, and hardly to be alleviated by remedies. It is paroxysmal, notwithstanding the unvarying character of its cause, in consonance with the tendency to periodical activity which prevails in the nervous system. Sometimes the pain is increased notably by atmospheric changes. The pain may sometimes be arrested by firm pressure upon the nerve above the seat of the tumor. In some cases pressure upon the neuroma, or even handling it, causes great pain. The intensity of the pain does not depend upon the size of the tumor, some of the smallest having earned the appropriate name of tubercula dolorosa. The continued irritation of a neuroma sometimes produces a condition of general nervous excitability, which shows itself in hysterical and even in true epileptic convulsions. Occasionally there are abnormal sensations (paræsthesiæ), formication, numbness, etc., in the distribution of the nerve affected, and when from pressure or histological changes the fibres are destroyed anæsthesia results.
The interference with the conductivity of the motor fibres, which occurs less frequently than alterations of sensation, shows itself in cramps, tumors, paresis, and paralysis, according to its degree.
Neuromas may destroy life by the continued excessive pain, which wears down the strength and depresses the vitality. Death may be caused by their peculiar situation; as, for instance, upon the cauda equina, where they produce paraplegia, paralysis of the sphincter and bladder, and trophic changes.
The DIAGNOSIS of neuromas can only be made when they are sufficiently superficial to be recognized by the touch, and along with the symptoms above detailed the tumor is situated upon the known course of a nerve, to which, moreover, its attachment allows a lateral movement.
The only TREATMENT available for neuromas is extirpation, which must be conducted with a view to sparing any fibres of the nerve not involved in the tumor. Where it is necessary to divide the nerve in the removal of the tumor, as small a portion as possible must be excised, with the hope of a regeneration and reuniting of the cut ends. The success of extirpation depends largely upon the nature of the neuroma. The true neuromas, while they often show a strong tendency to recur after removal, are benign and show no metastasis. For the false neuromas the prognosis will be in accordance with their benign or malignant character.