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SECTION III
NEUROSURGERY
CHAPTER X
ELECTRICAL EXAMINATIONS IN THE DIAGNOSIS OF PERIPHERAL NERVE INJURIES The importance of making a pathological as well as a clinical diagnosis of injuries to the peripheral nerves as a guide to surgical treatment was recognize dearly in the war, and consequently neurophysiologists concentrated their attention on this field in an effort to discover a means of accomplishing this purpose. Neurologists had been more or less content with determining what nerve was injured, and the site of the lesion. With the tremendous number of nerve injuries due to war wounds, it became imperative to attempt to decide in addition how much the nerve was damaged, as the treatment differed with the degree of injury sustained. Roughly one could separate nerve injuries pathologically into five groups: Contusion of nerve caused by missile passing through tissue near it without striking it; compression by scar tissue in infected wounds with secondary healing; hemorrhage into nerve without cutting fibers but with central neuroma; partial division with formation of lateral neuroma; complete division with formation of neuroma on the proximal end of severed nerve. A corresponding clinical differentiation was sought on the basis of care-ful motor, sensory, and electrical examinations. Physiologists familiar with the principles and application of electrical currents in diagnosis agreed that by this means such exact pathological information could not as yet be obtained, but felt that it was by developing this method of investigation more than any other that progress might he made. A considerable mass of experimental and clinical data to serve as a basis for further study was available as a result of the patient work of physiologists and clinicians of the nineteenth century. Galvani,1 in 1791, by his accidental discovery of the effect of an electrical current on a muscle-nerve preparation, laid the foundation for all the investigation that followed it. DuBois-Reymond, 2 applying the principle of induced currents discovered by Faraday, devised the faradie induction battery, an apparatus which is used to-day practically unchanged. In 1848 he made the important observation that it was not the passage of the galvanic current hut the changes in its intensity which caused muscular contraction. In 1849 Duchenne,3 of Boulogne, introduced electrodiagnosis with the faradic current, and defined the principles which guide its use to-day. Pflüger 4 established the laws which govern the differences in effect of the opening and closing contractions of the galvanic current. Remak,5 in 1865, stated "in some cases of completely paralyzed muscle and nerve, the strongest induction shocks do not excite muscular contractions, whilst a stronger effect than then norm accompanies the opening and closing of a constant galvanic current." The most outstanding addition to the practical value of electrodiagnosis was made by Erb,6 physiologist and clinician, who, in 1883, described the reaction
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of degeneration (De R) following complete nerve section. In his book are set forth clearly and completely the practical details of electrical examination and in it will be found many of the suggestions and facts rediscovered by later writers. D'Arsonval,7 near the end of the century, added to the therapeutics of electrical treatment the proper utilization of the heat generated by the galvanic current passing through tissues. Further contributions to our understanding of the principles underlying electrical degeneration were made preceding and during the years of the war by Sherrington,8 Lucas, 9 Adrian,10 Forbes,11 Lapicque, l2 and numerous others. A large part of this work has as yet no practical application to the clinical problem, but its value is unquestionable. Thus recent work has resulted in establishing the "all or none" principle of nerve response to stimulation; has demonstrated the return of a nerve impulse to its full intensity after passing diminished through an area of decrement produced by localized narcosis; has advanced the conception of the nerve impulse as deriving its energy fromthe nerve itself, similar to the burning of a fuse once it has been ignited; and has made a tentative separation of the nerve impulse to the muscle into an element maintaining position (static) and a part controlling motion (kinetic).Facts of normal nerve physiology such as these are the background upon which abnormalities can be judged and are therefore of great importance; but it must be confessed that practically they have not brought us measurably nearer to the possibility of making a diagnosis of the pathological condition of an injured nerve. There have been a few additions to our knowledge of a more practical nature which may safely be attributed to the interest aroused in this subject by the problems of the war. That the cathodal response is always greater than the anodal in stimulating normal nerves and is usually reversed in degenerated nerves has been known for a long time, but the explanation of this phenomenon has only recently been found. The experimental work of Cardot and Laugier 13 and of Bourguignon 14 has shown that the negative pole is always the active one on making the current, and that the electrical current invariably flows from the cathode to the anode. It is clear, therefore, that when the small stimulating electrode is placed in close proximity to the nerve, a greater response from the concentrated stimulus results, while, when the large, distant electrode is the origin of the current, a diffused and weakened stimulus reaches the nerve from it or from the secondary negative pole, which it causes to appear deep in the tissues. Furthermore, if the nerve is degenerated, the concentration of the current from the small active electrode upon it has little effect, while the relatively more greatly diffused current when the opposite polarity is used, due to its diffusion, stimulates the muscle over a wider area, thus accounting for the apparently greater reaction with the positive pole. Another important point which has recently received more attention is the increased irritability of the paralyzed muscle to direct galvanic stimulation, the quantity of current necessary for contraction being less than for the normal muscle. This statement requires qualification, for it holds true only for a few weeks after the nerve has been injured, and the response is obtained only by
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direct stimulation of the muscle at its tendon insertion and not through its nerve. The increase in galvanic irritability is coincident with increased mechanical irritability, or increased ideomuscular reflex, demonstrated by tapping the muscle. It is worth noting in this connection the interesting observations made by Langley15 that immediately following section of the nerve the paralyzed muscle is in a state of constant fibrillary twitching, during the time when rapid atrophy is taking place. The association of increased electrical and mechanical irritability, the constant fibrillarv activity, and the rapid atrophy when the nervous control of the muscle is removed are instructive as illustrating the loss of inhibition brought about by severing the connection between the anterior horn cell and the muscle. Practically it is possible to utilize this increase in irritabilitv in examination and treatment. The use of strong currents causes contraction of healthy muscles, which may be misinterpreted as the contraction of paralyzed muscles or may make it difficult to determine if the muscles which are being tested are responding. The use of the weakest current which will cause contraction in paralyzed muscles will help to eliminate this difficulty, as this intensity of current does not contract healthy muscles. Finally the importance of the duration of the application of a current necessary to produce a contraction in a normal muscle has been recognized, and the attempt to apply this knowledge to diagnosis has resulted in the addition to the instruments used for electrical examination of the condenser. It has been found that under fixed conditions for every muscle with a normal nerve supply a definite duration of stimulus is necessary for contraction with a minimal current. The slightest injury to the nerve causes an increase in the time required to produce a contraction with this minimal current, and the degree of injury is reflected in the relative increase in time. Adrian 10 has shown that the normal nerve has a "quick mechanism," responding to a very short stimulus, while the muscle deprived of its nerve requires a stimulus much longer, at least one-hundredth of a second. Expressed in figures it may be stated that a normal muscle will respond to electrical stimulus of 100 volts potential applied to its nerve for about one twenty-four-thousandths of a second. After injury to the nerve has taken place, the duration of the stimulus must be increased to from one five-hundredths to one one-hundredth of a second. The average faradic impulse lasts approximately one one-thousandth of a second, and this current therefore soon becomes ineffective as the nerve degenerates. To provide an instrument which will readily indicate the time necessary to produce a contraction, the condenser as adapted by Sir Lewis Jones,16 or some modification of it, has been brought into wide use. By using the discharge through a constant resistance of condensers of different capacity charged at the same voltage, a numerical value could be obtained of the duration of current necessary to produce contraction, and this recorded figure was then available as a basis for comparison on subsequent examinations. The value of this addition to our investigating instruments has been differently stated by various users, and widely different opinions have been expressed. It is agreed that it furnishes confirmatory evidence of nerve injury by showing the increased time necessary to produce a muscular response. It has been claimed that it has value in showing in which direction the injury to the nerve is pro-
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gressing, a gradual increase in time necessary to produce a response indicating a lesion which is increasing in severity and therefore requiring operation, and a shortening of the time, a tendency to spontaneous cure, contraindicating operative interference. It would thus have its greatest value as a measure of the progress toward recovery in cases of nerve injury where operation was postponed because a degree of function remained. An effort was made to gain further information about the condition of the nerve by noting the effects of stimulation of nerves exposed at the time of operation. This was accomplished by using specially constructed electrodes of two wires separated by beads and surrounded by glass tubing. Such an electrode can readily be sterilized. By the use of a weak faradic current the exposed nerve was stimulated directly, and if any response was obtained a partial lesion could be recognized and the surgical treatment modified accordingly. The large number of nerves which were exposed by war injuries gave an unusual opportunity to study the internal geography of the nerve by electrical stimulation, and it is regrettable that advantage was not more fully taken of the opportunity, as the knowledge gained is of inestimable value in the intelligent surgery of the peripheral nerves. However, a considerable number of observations were made, and these have supplemented the careful anatomical studies made by A. Stoffel,17 who was the first to show the great practical value of a knowledge of the internal topography of nerves. The methods of examination as actually carried out in Army hospitals devoted to treatment of cases of peripheral nerve injuries may have value as a matter of record. The apparatus used was chiefly: the Wappler galvanic-faradic plate equipped with a sliding induction coil of the DuBois-Reymond type, milliamperemeter, rheostat, and pole changer, and the modified Lewis Jones condenser. These instruments were connected with the lighting current. Whenever possible patients; were examined on return from the physiotherapy department, as the massage of the paralyzed muscles made their response to electrical tests more satisfactory. The room was kept warm enough to prevent chilling of the skin and the electrodes were covered with wet cotton or chamios skin so as to diminish skin resistance as much as possible. When testing with the galvanic, the current was allowed to pass for a while through the muscle before being broken, as suggested by Erb, a better response being thereby obtained. The bipolar method was used practically exclusively, the large indifferent electrode being placed on the sternum or spine and held by the patient, and the small one being manipulated by the examiner. The small electrode was equipped with a spring on the handle to facilitate making and breaking the current. To determine the polarity of the stimulating electrode in case of uncertainty, the ends of the connecting cords were placed in a glass of water, the negative pole being indicated by the ebullition of bubbles. The amount of current necessary to produce contraction was determined on the corresponding muscle of the opposite extremity. The examinations were recorded in terms of the individual observations, rather than in terms of the conclusions to be drawn from them. Where all the muscles supplied by a single nerve were paralyzed, this was recorded as a group; when only part of them were affected, the individual muscles were specified. Observations were
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recorded of the following facts: The presence of sensibility to faradic currents in the skin supplied by the nerve to be tested; the response of the muscle to stimulation with the faradic current at the motor point and directly over the body of the muscle; the response to stimulation of the nerve with the galvanic current; the character of the response of the muscle to stimulation directly at its tendon insertion as to speed and strength of response and the relative effectiveness of opposite poles. In some of the clinics the condenser examination was part of the routine. Examinations were made at about monthly intervals and the results charted on a specially devised blank outline. The conclusions drawn may be here briefly summarized. Loss of skin sensibility to the faradic current in the most distal area of distribution of a nerve, usually associated with a corresponding loss of deep pressure, vibratory, and joint sensibility, was almost regularly found to indicate complete interruption of the nerve. In the few cases observed which seemed to invalidate this conclusion two explanations were considered possible. Unless careful microscopic sections were made of the fibrous tissue which invariably was found in the gap of a severed nerve, one could not be certain that some aberrant fibers carrying sensation were not contained in it. The other possibility, and one which has a correct anatomical basis, is that anastamosis may occur below the site of the lesion between the injured nerve and one running parallel to it. The return of faradic sensibility to the skin was usually the first certain evidence of returning function. Loss of response to stimulation of the nerve or muscle with faradic current was invariably found with any degree of traumatic injury to the nerve sufficient to cause motor or sensory disturbances. Immediately following injury the motor and sensory loss was usually over a greater area than could be accounted for by the nerve involved. This condition might rapidly disappear or persist. In the latter case the faradic response readily disclosed which muscles were actually deprived of their nerve connections and which were functionally paralyzed. A normal response in all muscles to faradic stimulation, therefore, was considered to eliminate the possibility of peripheral nerve injury, the paralysis being in such case either hysterical or due to involvement of the central rather than the peripheral nervous system. The phenomenon described by Erb, in which faradic stimulation above the site of the lesion gives no response hut stimulation of the nerve below or of the muscle produces contraction. must be guarded against. This condition is interpreted as indicating either a functional blocking of the nerve due to compression or an injury so recent that secondary degeneration is not complete. Kraus 18 has called attention to a similar phenomenon on stimulation of the exposed nerve. Return of voluntary motion invariably preceded the return of response to the faradic current. Stimulation of the injured nerve with the ordinary galvanic current also failed to give a response no matter how mild the lesion, and this method of examination, therefore, tells us nothing about the pathological condition of the nerve. It is in this part of the electrical examination that the condenser was expected to yield information of value, for by increasing the duration of the current a reaction could be obtained when the nerve was not completel-
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interrupted. The modified Jones condensers used in the Army hospitals were graded to give a discharge at, 100-volt potential from 0.01 microfarad to 2 microfarads. Normal muscle gave a response to the shortest of these discharges. Following injury the duration had to be progressively increased as degeneration of the nerve took place. Of course, when division wtas complete and followed by secondary degeneration, no length of condenser current gave a contraction. The changes observed by direct stimulation of the paralyzed muscle with the galvanic current, were of the greatest. value. Uniformly the muscle failed to respond when stimulated over its motor point, but responded with increased irritability when the electrode was applied over the insertion of its tendon, giving the so-called "longitudinal reaction." The response was delayed, wavelike, or creeping in character, and in general the degree of slowness was an indication of the severity of the lesion. Thus the contraction immediately after injury was still quick, but became slower as the nerve degenerated, and the reverse process took place as the nerve gradually regenerated. When muscles remained without treatment for a prolonged period, such fibrosis might take place that, very slight or no contraction could be obtained. This condition warranted a poor prognosis. Occasionally stimulation with the galvanic current gave a tetanic contraction. This phenomenon has been recognized for a long time in the literature of the subject, but no explanation is given for it. Since it occurred with all degrees of nerve injury, its occurrence could not be used as a diagnostic criterion. Finally a reversal of polarity was commonly found associated with a completely interrupted nerve; that is, the contraction obtained with the anodal closing current was greater than the cathodal closing current. While this phenomenon was occasionally observed in normal muscles, no confusion resulted, as other signs of injury to the nerve were always essential to make a diagnosis of nerve injury. It has been stated by some observers that massage will change the polarity of a muscle. It was assumed, then, that when the application of the faradic current over the sensory distribution of a nerve was not perceived, and the muscles failed to respond to stimulation with this current, when galvanic and condenser current failed to cause contraction, and muscle stimulation with the galvanic current over its tendon insertion showed an increased contraction of a wavelike, creeping character, with reversal of polarity, a diagnosis of complete interruption could almost safely be made. Partial interruption or compression would be indicated correspondingly by fewer of these signs. In summarizing the work on electrical examinations, the question that naturally arises is, does this method of investigation give sufficiently accurate and valuable data to the surgeon to repay him for the time spent in carrying it out? Conservative opinion seems to be agreed that this question can he answered in the affirmative. Its greatest value, surely, is in the period which follows shortly after the injury, when with complete motor and sensory paralysis a reaction of degeneration would influence the surgeon to early operative interference. It must be confessed that when such a condition remains stationary for six months or longer, an electrical examination is no longer needed to determine the advisability of operation.
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REFERENCES
(I) Galvani, Aloysius: De viribus electricitatis in motu musculari commentarius cum Joannis Aldini dissertatione et notis. Mutinae, apud societatem typographican, 1792.
(2) Du Bois-Reymond, Emil: Untersuchungen über thierische Elektricität. G. Reimer. Berlin, v. 1, 1848, 258: 447.
(3) Duchenne (de Boulogne): Exposition d'une nouvelle méthode de galvanisation, dite galvanisation localisée. Archives généerales de medécine, Paris, 1850, xxiii, 257: 420.
(4) Pflüger, Eduard: Ueber die tetanisirende Wirkung des constanten Stromes und das allgemeine Gesetz der Reizung. Virchow's Archiv für pathologische Anatomie und Physiologie und für klinische Medicin, Berlin, 1858, xiii, Nos. 4-5, 437.
(5) Remak, Robert: Application du courant constant au traitement des névroses. Germer Bailliére, Paris, 1865.
(6) Erb, Wilhelm: Handbook of Electrotherapeuties; translated by L. Putzel. William Wood & Co., New York, 1883, 74.
(7) d'Arsonval, A.: Production des courants de haute fréquence et de grande intensité ; leurs effets physiologiques. Comples rendus hebdomadaires des séances et mémoires de la sociéte de biologie, Paris, February 4, 1893, 9 s., v, 122. Also Nouveaux modes d'application de l'énergie électrique: La voltaisation sinnsoidale; Les grandes fréquences et les hauts potentiels. Bulletin de l'académie de médecine, Paris, March 22, 1892, 3 s., xxvii, 424.
(8) Sherrington, C. S.: Break-shock Reflexes and "Supramaximal" Contraction-response of Mammalian Nerve-muscle to Single Shock Stimuli. Proceedings of the Royal Society of London, Series B, London, 1921, xcii, No. B 246, 245.
(9) Lucas, Keith: The Conduction of the Nervous Impulse. Longmans, Green and Company, London, 1917.
(10) Adrian, E. D.: The Electrical Reactions of Muscles before and after Nerve Injury. Brain, New York, 1916, xxxix, Pts. 1 and 2, 1. See also Adrian, E. D. and Forbes, A.: The All-or-nothing Response of Sensory Nerve Fibers. Journal of Physiology, Cambridge, 1922, lvi, No. 5, 301.
(11) Forbes, A., Ray, L. H., and Griffith, F. R.: The Nature of the Delay in the Response to the Second of Two Stimuli in Nerve and in the Nerve-Muscle Preparation. American Journal of Physiology, Baltimore, Md., 1923, lxvi, No. 3, 553.
(12) Lapicque, Louis: Sur l'interpretation des électromyogrammes. Journal de radiologie et d'électrologic, Paris, 1923, No. 6, 249.
(13) Cardot, H.. and Laugier, H.: Localisation des excitations de fermeture dans la méthode unipolarie. Comptes rendus hebdomadaires des séances de l'académie des sciences, Paris, Feb. 5, 1912, cliv, 375.
(14) Bourguignon, G.: La forme de la contraction a l'état normal et pathologique. Journal de radiologie et d' électrologie, Paris, 1914-1915, i, No. 5, 261.
(15) Langley, J. N.: Remarks on the Cause and Nature of the Changes which Occur in Muscle after Nerve Section. Lancet, London, July 1, 1916, ii, 6.
(6) Jones, H. Lewis: The Use of Condenser Discharges in Electrical Testing. Archives of the Roentgen Ray, London, 1913, xvii, No. 12, 452.
(17) Stoffel, A.: Zum Bau und zur Chirurgie der peripherenu Nerven. Verhaṅdlungen der deutschen Gesellschaft für orthopädische Chirurgie, Stuttgart, 1912, xi, 177.
(18) Kraus, Walter M., and Ingham, Samuel D.: Peripheral Nerve Topography. Seventy- seven Observations of Electrical Stimulation of Normal and Diseased Peripheral Nerves. Archives of Neurology and Psychiatry, Chicago, 1920, iv, No. 3, 259.
