A system of practical medicine. By American authors. Vol. 5

by Unknown

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.