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.