942
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
943
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
944
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-
945
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
946
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-
947
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.
948
REFERENCES
(I) Galvani, Aloysius: De viribus
electricitatis in motu musculari commentarius cum Joannis Aldini
dissertatione et
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(2) Du Bois-Reymond, Emil: Untersuchungen
über
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(3) Duchenne (de Boulogne): Exposition d'une nouvelle méthode de
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(4) Pflüger, Eduard: Ueber die tetanisirende
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(5) Remak, Robert: Application du courant
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Contraction-response
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(13) Cardot, H.. and Laugier, H.:
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(14) Bourguignon, G.: La forme de la
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(15) Langley, J. N.: Remarks on the Cause and
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(17) Stoffel, A.: Zum Bau und zur Chirurgie
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