LECTURE III.
ELECTRICITY IN DIAGNOSIS AND TREATMENT.
A.—Electricity in Diagnosis.
Gentlemen,
Electro-Diagnosis.
Our first two Lectures were devoted to a consideration of electrical instruments; the different varieties of electricity; and the most approved methods of applying them in therapeutics. To-day we have to study their uses in diagnosis, prognosis, and treatment.
Test of Electro-Irritability.
The chief use of electricity in diagnosis is dependent upon its power of evolving muscular contraction. We have seen—as I demonstrated to you upon my left forearm—that both muscles and nerves, when in a normal condition, respond to the stimulus of electricity. In disease this response, or irritability, may remain unaltered, or it may be increased, decreased, or abolished; and our first step in electro-diagnosis should therefore be to ascertain the exact condition of electro-contractility. As in practically almost all our cases we have to do with altered reaction existing only in one nerve or muscle, or in one of two symmetrical groups of nerves or muscles, we possess a ready means of testing irritability by ascertaining its relative condition upon opposite sides of the body, as, for example, in an ordinary case of hemiplegia.|Test of Farado-Irritability.| In examining such a case electrically—and the principles of procedure are the same in all cases—it is convenient to commence our investigation with the Faradaic current, and to ascertain the lowest power which will call into action any one of the muscles of the healthy side, and then to apply this same strength of current to identical points of the corresponding muscle on the diseased side, noting whether it causes contraction. If so, we decrease the power of the current, when if contraction still occurs there is increased irritability, or vice versá, as the case may be. Having ascertained the condition of the muscle we proceed similarly to test its motor nerve, for we shall see hereafter that in certain diseased conditions muscle and nerve irritability are affected unequally. One conductor being held to an indifferent part of the body we apply a fine-pointed conductor to the most superficial point in the course of the nerve, in the way that, as you will recollect, I electrized my left median nerve. |Test of Voltao-Irritability.| We next submit the muscle and nerve to similar examination with the Voltaic current. Holding both conductors immovable, we interrupt the current for a moment by moving the “key” of our battery, or if it is not provided with a key, while one conductor is stationary, we break the current by lifting and reapplying the other. It is essential that on both sides there should be exact similarity in the application, and that the electrodes should be placed on identical points of the muscle, and this is especially important with the Voltaic current, for healthy muscle responds to it more readily when it flows down the limb, that is, with the positive pole nearest to the spine, and the negative farther from it than when it flows up, and consequently a reversal of the poles will influence the result.|Rule for strength of Current.| In testing a case in which there is equal disease upon both sides—as in some cases of paraplegia—we must be guided by a knowledge of the strength of current usually required to induce contraction. As a general rule, unless a current that causes energetic and painful action in the muscles of the ball of the thumb produces some contraction, irritability is impaired. If, in our examination of the muscle, we find irritability normal to both currents, we have proof of the integrity of the muscular tissue. If the muscle also responds by contraction to electrization of its nerve, we have further proof that the nerve is healthy, and also the spinal cord at the point of origin of the nerve.|Electro-Irritability diminished.| If we find the irritability lessened, there is disease of either muscular tissue, nerve or cord; and, as a rule, this will be in direct proportion to the amount of diminished irritability. |Electro-Irritability increased.| Increased irritability points to increased vascularity or irritative lesion; but in such cases we very seldom require the aid of electricity to complete our diagnosis.|Voltao-Irritability increased.| The reactions of Faradism and Voltaism are usually equal, but in some cases in which muscular response to Faradism is diminished or abolished the muscular reaction to an interrupted Voltaic current is not only preserved but increased. The diseased muscle will respond much more readily to the Voltaic current than the corresponding muscle of the healthy side; while at the same time it will be found on examining the nerve that there is equal diminution to both currents.|Diagnosis of Peripheral from Central Disease.| This increased muscle reaction is due to the special irritability of muscular tissue, and is quite independent of any nerve influence. It exists only in peripheral and never in central lesion, and by it we obtain an absolute diagnosis of such cases as local paralysis of the facial nerve from facial hemiplegia, paralysis of the extensors of the wrist and fingers, due to lead poisoning, from commencing muscular atrophy, or progressive muscular atrophy from paralysis from section of a nerve—all important questions as affecting treatment. |“The Degenerative Nerve Reaction.”| It is known as the “degenerative nerve reaction,” as it always follows when a nerve trunk is involved in the lesion. There is then diminution of Faradaic irritability through both nerve and muscle, diminution of reaction to the Voltaic current when the rheophores are applied over the nerve, and increase of reaction when they are applied over the muscle; but there is no relation between these interesting variations in the electrical condition of nerve and muscle, and the degree of paralysis to the will, for there may be perfect muscular paralysis, as in hemiplegia, when the electrical condition of both nerve and muscle is unchanged; but, on the other hand, in muscles equally paralyzed we may find absolute electrical changes in some, and none in others. We may often positively predict that these latter will rapidly recover—one instance of the use of electricity in prognosis.
After long disuse of healthy muscles a slight degree of diminution of electric irritability may sometimes be present, but this is always restored by two or three Faradizations, and its existence is hardly likely to present any difficulty in diagnosis. |Central Paralysis.| With this qualification we find that in paralysis from brain disease electric irritability is normal, except when irritative lesion is present, and then it is increased.|Spinal Paralysis.| In paralysis from disease of the substance of the cord irritability is diminished, and this will sometimes aid us in the diagnosis—not always easy—between commencing paraplegia and locomotor ataxy. In ataxy—at least in its early stages—irritability is normal. In progressive muscular atrophy it is normal as long as any muscular tissue remains.|Hysterical Paralysis.| In hysterical or emotional paralysis irritability is normal, but electro-sensibility is often much impaired. |Diagnosis between Real and Feigned Disease.| |Electricity as Proof Positive of Death.| These variations will sometimes enable us to distinguish between real and pretended disease; and, finally, absolute abolition of electric irritability in all the muscles of the body is proof positive of death, so that those extraordinary people who are haunted by a fear of being buried alive may rest contented if they provide that after apparent death, and before burial, their bodies shall be submitted to thorough electrical examination.