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.