Since their introduction into clinical medicine almost
50 years ago.
The techniques of Electro biography have added
immeasurably to the recognition,
understanding and direction of therapy of neuro muscular
disease in man.
What I shall attempt this afternoon is a
definition of some of the techniques that are useful in
vivo.
I shall review their application limitations
and value in disorders of the motor unit,
and I shall attempt a prophecy of some of the innovative
developments of recent years.
Therefore this is by no means a compendium of a field that
has already nurtured five International Congress is
one in which several standard texts are extended.
I shall try to give you some of the field for the
fact that E.
M.
G.
Must be clearly tailored to the clinical problem of the
patient as a fishing expedition.
It is rarely fruitful as an exercise in
clinical physiology.
It is often exciting if we can go to the
first slide
on this are depicted the various levels of the nervous
system pathology at any
level of which may lead to a complaint of
weakness.
The techniques of electro biography have their
most application,
their highest application in the motor
unit,
which is all you all of you recall,
is the anterior horn cell.
It's peripheral extension,
the motor nerve fiber,
the neuro muscular junction and all of
the muscle fibers supplied by a given anterior horn
cell.
We go to the next slide,
we can see that at the level of peripheral
nerve.
There are several techniques which are
useful for studying the health of nerve.
Basically these have to do with the
measurement of conduction velocity of nerve in
motor mixed and sensory nerve fibers and the
excitability of peripheral nerve.
The next slide,
please this slide
attempts a schematic representation
of the techniques of nerve conduction velocity.
Perhaps it is a bit simplistic,
but I believe if one understands the simple
factors behind the measurement of motor nerve conduction
velocity,
then some of the difficulties in the application of
this technique become apparent.
Under ordinary circumstances,
a nerve is selected that may be stimulated
distantly and proximately in
order to give rise after a latent
period to a muscle action potential.
Now one would think that if velocity is distance per
unit time,
that all that needed to be done would be to measure the
time from the stimulus to the response,
divide that into the distance between
stimulating point
and recording point and come up with a
velocity.
However,
the basic tenants of physiology
have us to understand that nerve conduction
velocity,
in which we are interested is a
phenomenon which in normal
individuals occurs
at a magnitude of 40 to 60 m per
second,
whereas muscle conduction velocity
occurs in the range of 4 to 6 m
per second.
Thus one doesn't know where the nerve impulse leaves
off and the muscle impulse starts.
For this reason one must
subtract the latency
from a distal stimulus
from the total latency from a proximal
stimulus to come up with a latency difference
that can be divided into the distance between
stimulating electrodes and a
velocity derived
two other points should be evident from this slide
that not only velocity can be calculated in this
fashion,
but also one can look at the
distal latency itself,
and one can as well look at the amplitude or
size of the muscle action potential.
Since velocity is distance per unit
time,
one would think that one could draw a
plot between distal distance
and distal latency And
have a straight line relationship between the two.
This is not true for distal distances
rather over a wide range of
distances.
Distal latency occurs within a
fairly narrow band.
The absolute value of distal latency,
therefore is quite important,
irrespective of the distance over which the stimulus
occurs.
That absolute value may be the only
indication of disease in nerves
which is much more prominent distantly.
Likewise,
the amplitude of the muscle action potential
itself may be a measure of the number of nerve
fibers that are stimulus bill,
or the number of muscle fibers which respond
to that stimulus.
In ordinary circumstances,
that amplitude is expressed as a million volt
phenomenon of the negative peak of
the action potential on occasion as a peak to
peak amplitude.
Later,
I think we shall see that with
certain conditions of stimulation,
the amplitude may appear to increase
while the duration
of the response decreases the
total area,
therefore not changing
Edward Montgomery about two years ago introduced a
technique for the automatic analysis
of evoke muscle action potential
area in the hopes that this would be a
better measure of neuromuscular
disease.
Unfortunately,
in normal subjects,
the range of area is as great or greater
than the range of amplitude itself.
With that as a background.
Let us go on to some of the applications of nerve
conduction velocity in the next slide,
which are a series of data obtained from a
patient with the G.
In barre syndrome of idiopathic pollen iritis.
One can see that in the early
stages of this illness on
occasion with proximal stimulation,
the response is often quite small and broken
up,
whereas with distal stimulation it is fairly
large.
This difference becomes apparent as the
disease progresses but then is
repaired so that in health
at time d hear the response to a
to a distal stimulus was about the same size
and shape is that to a proximal stimulus.
You will note that the latency
two onset of distal stimulus at the
height of the disease when the patient was first studied
was quite prolonged compared to the
latency in recovery.
Thus,
distal latency in this instance was an
indication of neuropathy.
These data are graphed out in the next slide
with conduction velocity,
showing at the top of the graph versus
time distal
latency in the middle graph and
evoked muscle action potential amplitude.
With distal stimulation shown with the
crosses and proximal stimulation shown with
the open circles In this
particular patient changes in all three
Parameters occurred.
The initial study showed a very small action
potential that improved as the patient
improved with a prolonged distal latency that
even got worse during the course of his illness,
only to return to normal values and with the
conduction velocity that at least for
onset muscle uh
latency differences was close to
normal range but dipped down to clearly
abnormal range is only to
return as the patient's strength improved.
This pattern of change in velocity,
latency and amplitude in the next
slide can
be plotted against
the months that it takes to recover
and although the data are kind of scattered,
a fairly straight line relationship
With a correlation value that is not
unrestricted ble can be seen from a
series of 40 patients studied the
University of Kentucky Medical Center over the past
nine years.
In this instance,
it was of interest that the patients with the slowest velocities
have the shortest kind of illness.
The summary of this application of motor
nerve,
conduction velocity would be that it has
great role,
a great role to play in certain kinds of
neuropathy.
But in the next slide,
The problems faced with this technique in other kinds
of neuropathy should be evident.
These data are taken from a paper by PK Thomas
that appeared in the Lancet in 1959.
At the top are shown data
from patients in chronic renal
failure and at the bottom.
Normal controls on the left hand side and
upper extremity nerve,
the median nerve and on the right hand side,
a lower extremity nerve.
The lateral pop little nerve.
Although the patients with chronic renal failure
show a general skew of their velocities
towards slower velocities.
I think it is readily evident that many
your E.
Mc patients with obvious clinical neuropathy had
velocities within normal range
in the next slide,
this problem of overlap cannot be
gotten away from with
serial measurements in this slide
at the top are taken data from a paper that appeared in the
new England Journal about five years ago.
The patient whose data are reported here
was quite seriously ill
in renal failure with neuropathy at the time the
initial media nerve conduction velocity was taken.
Renal transplantation was performed then
and over the next several months
improvement occurred and improvement in his
velocity occurred.
The authors who published this data offered this as
evidence for a technique to document
changes in a condition known to
be associated with neuropathy.
The data at the bottom of the slide are taken
from a paper that a medical student at the
University of Kentucky published
About seven years ago.
These particular data are serial observations
on a classmate of his who was no weaker at the
beginning of the study than he was at the end of the study.
The point of this slide is that even
serial observations may show a random
change that is as great as or
perhaps even more than the
observations from subjects with
neuropathy.
Therefore,
there are limitations to the measurement of motor nerve conduction
velocity in identifying
patients with clear and unequivocal
neuropathy,
and how do we overcome these limitations?
Let us look at the next slide.
It has been suggested that one way to overcome the
limitations is to look not only at the
direct or M,
or muscle response to nerve stimulation in this
instance distantly and here
approximately,
but to look at a late wave as
well,
a wave which takes longer to occur the
further away from the spinal cord one
stimulates and a wave therefore which
is reflex in character.
Richard Meier showed very nicely about 10 years
ago that this waveform occurred in the upper
extremities of patients whose dorsal nerve
roots had been sectioned for the control of pain
in carcinoma and therefore that this
small muscle,
small muscle or F wave was
a axon axon reflex
occurring with anti drama,
traveling up the motor nerve through the motor nerve
root and back out again Ortho dramatically
from that initial stimulus.
The latency over this much longer
distance is a fairly regular phenomenon
and disorders which selectively affect the nerve
root may prolong that latency.
And so just as distal latency may may may be a
measure of distal neuropathy.
So,
to F wave latency,
in the presence of normal velocities may
give a clue to the presence of neuropathic
weakness.
If this sort of technique is normal,
what else can be done in the next slide?
A schematic representation of a nerve action
potential,
which is multiphasic.
As one can see here with nerve
stimulation can be seen
look tall and Rosenfeld.
Using averaging techniques with
multiple sensory nerve stimuli
have shown that one can in
the intact human subject record a
compound nerve action potential
whose various
components can be measured in terms of their
velocity and in terms of the amplitude of
the envelope conducting at that velocity.
And they have shown very nicely in a paper reported in
brain in 1972,
a strong correlation between
the changes either in
velocity of one or another of these components
or in the amplitude of the envelope and the
histological appearance of that neuropathy.
Since many Europa these are purely sensory.
This technique of compound nerve action
potential study is a very
useful adjuvant to the analysis of
peripheral nerve disease.
Other techniques are shown in the ensuing slides.
The next slide,
please Here is graft
the thesis behind the measurement
of nerve excitability,
which Wilson described in the journal of neurology
neurosurgery and psychiatry more than 10 years
ago.
If one relates the intensity of a
stimulus required
to elicit a
threshold nerve action potential,
giving paired stimuli at
various intervals and
relating the intensity of the
second or test stimulus.
Following a super maximal
conditioning first stimulus,
one is able to define the absolute refractory
period as the time during which a
second stimulus,
no matter how intense will not elicit a
second response,
the relative refractory period with the two
stimuli or equal intensity and a
following period called super normal
period where the second
stimulus needs to be even less than it
is without the conditioning stimulus.
I think you can tell or deduce from the description
of this technique that it is a very meticulous one
requiring a great deal of time.
And so in the next slide
James Heckman,
then a medical student at the University of Kentucky
decided to re approach the old
concept of a strength duration curve.
He noted that with the standard stimulator
available for measuring strength duration curves
uh in the normal
fashion that any fizzy interest
will use that stimulator while it could
give a square wave that very brief stimulus
durations had to have a superimposed
R.
F.
Wave to give a pseudo square wave at
longer durations.
Thus,
using this stimulator,
one doesn't know really at what level the stimulus
is at any moment during this long
stimulus.
Using a different light isolated stimulator.
Even at the long intervals,
a quite square wave was elicited and in
the next slide,
if one compared stimuli of
varying strengths from this light
isolated constant current stimulator over
varying durations,
one was able to depict a
so called excitability curve.
The response in the instance of the
excitability curve was the nerve action
potential elicited by per cutaneous
nerve stimuli When Heckman
compared these data In the same
patients,
or at least five out of the six of the same
patients with a standard strength duration
curve.
He noted that this excitability curve
was significantly more
sensitive to this parameter of nerve
function than the standard strength duration curve
in the next slide.
Elizabeth right,
extending his technique even further has
shown that there is a range of normal
values depicted in the crosshatched area
here against which can
be compared a group of patients
who have normal nerve conduction
velocities but obvious clinical
neuropathy,
their conduction velocities did not pick out the
neuropathy.
This excitability curve clearly did,
especially at the long duration stimuli.
This technique has been of a special use in the next
slide in the analysis
of peripheral nerve function in patients and
chronic renal failure,
where it can be seen That of a group of
19 patients who had clinical neuropathy.
Their upper extremity ulnar nerve conduction
velocity was outside normal
range only seven out of 19 times
the perennial nerve conduction velocity was
rather more sensitive.
But ulnar nerve excitability
identified every patient with neuropathy,
there is a problem.
Clearly in the excess
sensitivity of both of these techniques.
Since certain numbers of patients without clinical
neuropathy in your E mia will have slow
conduction velocities or decreased
excitability.
I think it should be recalled that nerve
biopsy of all patients in your E.
Mia in some studies will show clear
cut changes.
Histological E what Hickman's technique was
after was a clinically useful way of
approaching and identifying the patient who will
have neuropathy or who may go on to develop it.
And in the next slide,
this question was looked at.
Eight patients having serial studies
showed a slow peroneal nerve conduction
velocity before the onset of their
neuropathy only in 25% or
two out of eight of the times.
Whereas six out of the eight patients had
decreased excitability.
This technique is in its infancy as a clinical
tool,
but may,
together with the book tall way of looking at
compound nerve action potential,
be an extension of nerve function with electro maya
graphic techniques.
Let us go on to the next slide.
Another extension has been developed
by McComas and his colleagues
initially in London and
subsequently in Ontario.
They have noted that if a peripheral nerve is
stimulated and recording made from a
muscle supplied from that nerve
with a reference electrode in this instance,
on the foot and a ground strap between the
two.
In the next slide
that with increasing strength of
stimuli,
increasing size of surface
recorded muscle action potentials can
be had.
If one looks at a reference electrode placed
elsewhere on the foot.
This particular extension digitally umbrellas muscle
is the only muscle responding to perennial
nerve stimulation and that perhaps is why
they have chosen this preparation for most
of their approach.
Using threshold stimuli,
one can define a
minimal motor unit
size and in McCormack's
technique.
this is referred to as the size of a
single motor unit.
One can therefore divide into the
maximal response this single
size to come up with a measure of the number of
motor units in that particular
patients extensive digital and bravest
muscle.
And what does this technique show us in the next
slide?
If one looks at control subjects,
the amplitude of their motor unit,
the size of the motor unit with the McComas
technique is about the same as it is
with limb girdle muscular dystrophy,
and in fact,
there may be some skew toward increasing
amplitude of potentials
in spinal muscular atrophy.
There are many potentials which are of significantly
larger amplitude,
so that in McComas hands,
the individual amplitude is
perhaps of help in clearly
neuropathic disorders,
but not of much help in the limb girdle,
muscular dystrophy,
and other dis trophic disorders.
But what is more amazing in the next slide,
if one looks at the number of units
from the extensive digital and bravest muscle in
control subjects compared to a
series of disorders which
are at least traditionally held to be
my opa thick one is struck that the McComas
technique shows a drop out in the number
of motor units.
Now that's supposed to happen only with
neuropathic disease.
And so in the next slide,
McComas has hypothesized that
neuro muscular or motor unit
disease may derive
from a change in the motor unit,
which ultimately
occurs because the motor neuron itself
becomes sick.
And as that sickness progresses,
single fibers drop out until
generalized atrophy occurs and whole motor
units are lost.
It is this hypothesis which electrically
gives support to the concept
that much,
if not all,
of motor unit disease is ultimately
neural in character.
In the next slide,
there are some who take issue with this
particular way of looking at things and if
they compare their control data in terms of
motor unit potential amplitude with a
variety of muscular dystrophy ease.
And in this particular instance most of them were
classic Duchenne dystrophy ease.
I think it is fairly evident that the size
the individual units with the McComas
technique is here clearly shifted towards
smaller units,
looking at the total number of units,
and I do not have a slide to show you from this
author showed a a
similar number of motor units.
And so the McComas technique supported
what standard electro media graphic techniques had
suggested in the past.
I would simply summarize my discussion of this
technique by saying that there are many questions.
It raises questions which are not yet answered.
In the next slide,
we go to the next level of the motor unit,
the neuro muscular junction and at this
level the response to repetitive nerve
stimulation is the hallmark of a
change of a sickness that may be
productive of weakness.
The next slide
shows us the basic principle on which
clinical E.
M.
G.
Analysis of neuro muscular transmission is
based.
In this instance,
a nerve stimulus is applied to the whole nerve
supplying many motor units and a muscle
action potential recorded with surface electrodes.
In this instance it is of eight million volts
theoretical amplitude as far as the
negative wave is concerned if
during the course of repetitive super maximal nerve
stimulation,
motor units drop out as indicated
by the black marks.
Here the evoked action
potential amplitude will decrease and
one can express The
change during repetitive stimulation
as a proportion in
this instance,
a 50% block in the next
slide,
this change is nowhere more clear
than in the illness.
Myasthenia gravis,
in which paired stimuli At
intervals less than 1/2.
In this instance,
100 and 60 milliseconds show a fall
off in the amplitude of the second stimulus.
In all instances the stimuli are super
maximal for nerve you have
heard earlier and I'm sure recall that
the classic hallmark of Myasthenia
gravis is a fall off during
repetitive stimulation that repairs
itself early on in the course of repetitive
stimulation.
In this instance,
at 10 impulses per second.
This so called early dip is seen
classically in myasthenia gravis and only in
one other setting in individuals
who have been given a small amount of your
r if the stimulation is continued for a
long time,
the fall off with a late exhaustion is
observed and both of these phenomena can be
ameliorated if colonist arrays inhibitors are
given in the next slide,
it is important to be certain that the response in
muscle to nerve stimulation does not
arrive at other levels.
One way of looking at this is to apply a
stimulus through a needle electrode in the
distal portions of muscle away
from the zone of innovation.
The motor point and to record with needle
recording electrodes at two points are one
here and our two here.
In this instance,
the same repetitive stimulation was given
and the response,
aside from a little baseline artifact,
was the same to the initial response as it was
during the course of stimulation.
There was a little change in conduction velocity during
repetitive stimulation,
but the amplitude,
the size of the evoked response response
in muscle to muscle stimulation stayed the
same even though,
as we saw in the former slide,
it changed with nerve stimulation
so much for the theory behind the analysis of
neuro muscular disease.
Let us go on into the next slide.
This kind of technique can be
applied to the study of Children
born of my aesthetic mothers and I
think in the case of the data on the
right hand side,
from a child who had transient neonatal
myasthenia,
one can see it fast rates of stimulation
and its lower rates the early dip
phenomenon once again,
and in the case of a child born to
a another mother with myasthenia,
but a child not manifesting clinical weakness.
No such early dip was observed.
This is therefore a useful technique for
the uncovering of myasthenia gravis.
In the next slide
There are a certain proportion of patients,
however,
who will not show any change
with repetitive stimulation.
Dr.
Young and his associates have estimated that if one looks at a
single nerve muscle
junction preparation in Vivo,
that the incidence of abnormalities even in the
presence of defined Myasthenia is of the order of
60%.
If you look at two or three or more neuromuscular
junctions,
that incidents can be increased to 85,
perhaps 90%.
But the remaining portion of patients who have
classic myasthenia in whom repetitive
stimulation will give no abnormality
for this reason Colin Brown reintroduced a
technique of Regional Cure Ization,
in which the same stimulus and recording
parameters with an intervening
uh ground
strap are observed and under
tourniquet conditions,
an intravenous infusion of a small amount of
Harare is given after a latent
period.
The tourniquet is released and after four
minutes or so permitting restoration of
normal function.
Then studies of neuro muscular
transmission are had in the next
slide data from his paper in
the Journal of neurology neurosurgery and
psychiatry this year show what happens
in three normal subjects.
The response to repetitive stimulation before
the administration of cure are at rates
of two stimuli per second show no
change afterwards.
There is a minor fall off in
the total amplitude of the response,
but repetitive stimulation really doesn't do very
much.
But if we look at this in my aesthetic subjects in the
next slide one can
see that although ocular my aesthetics
may not show very much change.
Patients with generalized weakness,
even though it may be mild without any
evidence of change with repetitive stimulation to start
with may show a complete and total block
with very small doses of cure our
regional cure Ization therefore
may help to identify the 10 or
15% of patients with
classic myasthenia who do not show a
defect on repetitive stimulation.
The next slide
not only is the detrimental response
occasionally seen,
But there are conditions in which very
slow stimulation.
In this instance,
one per second will show a
fall off,
but very rapid stimulation.
In this instance,
20 per second will show a marked
increase in the amplitude of the
response.
The next slide shows that this
increase may in part be due to the
narrowing of duration and increase in
amplitude.
The so called bunching phenomenon,
but that if one looks at the response at the
end of this stimulus train at 10
cycles per second and compares it to
the beginning.
Not only is it shorter,
but also it is significantly larger in
area I.
E.
The increase in amplitude is even more than one
would expect from the bunching phenomenon.
That's important to realize because a certain amount of
facilitation,
perhaps up to as much as 20% can be
seen in normal subjects because of bunching.
This phenomenon of increase with fast repetitive
stimulation is what one would expect
theoretically with a defect in acetylcholine
release.
And these two slides have been taken from the classic
defect in acetylcholine release
that associated on occasion with a small cell
carcinoma of the bronchus,
the Eaton lambert syndrome.
In the next slide,
a similar defect can be seen particularly
with fast repetitive stimulation and in this
instance the
enhanced potentially ation or facilitation and muscle
action potential amplitude is expressed as a
percentage of baseline stimulation during and
after a train of repetitive stimuli.
The marked increase to 2.5
to 4 times the amplitude
occurred in this young man seen in the next slide,
who,
when he was admitted to hospital,
had a very blank face with immobile
eyes and dilated,
fixed pupils that would not respond to
light seen in his hometown
of Stinking Creek Kentucky.
Two months after this,
he was a tasseled haired little boy with
quite evident open eyes,
fully mobile,
not only in his ocular and bulb our muscles,
but also elsewhere.
It is likely,
although not proven beyond the shadow of a doubt that
this child's pre synaptic defect in
acetylcholine release was caused
by the presence of botulinum
toxin in some of the food found
near of his home.
In the next slide,
a response halfway between
myasthenia and
the pre synaptic defects we've been
considering can be seen on
occasion in this
instance an individual who became weak
after the administration of a polyp
peptide and an amino black aside antibiotic
was studied not only was nerve
stimulation given and muscle action potential
recorded,
but also the anti drama nerve action
potential was recorded during repetitive
stimulation.
Thus in this instance the change which is
occurring in muscle action potential was not seen in
the nerve action potential and hence must
be at the neuro muscular junction.
This patient's response started off quite
small and got seriously
smaller with repetitive stimulation at
slow rates with faster rates.
The rate of decline was not so great.
It wasn't a full potential ation But
at least faster rates of stimulation
overcame some of the block present in
this instance when stimuli were given one every 10
seconds.
This defect has been shown with single
fiber E.
M.
G.
Studies in vitro to
be associated with disordered pre synaptic
acetylcholine metabolism.
The next slide,
please.
I think it's important to call to mind
the character of the defect once again
with the early dip and late fall off during
repetitive stimulation at varying frequencies.
Because this hallmark of
myasthenia gravis in the next slide
Was what was clearly shown by Patrick and
Lindstrom in their classic paper in science
in 1973,
in which they showed that Myasthenia gravis
could be induced in laboratory
animals by the administration of
purified receptor protein.
In the next slide,
the MG defect in such an animal is seen
much more clearly during
and after repetitive stimulation,
where an immediate post titanic facilitation sometimes
occurs with a later post titanic fall
off.
This defect can be seen to be changed
by the administration of a colonist arrays inhibitor
in the rabbit.
The point I'm trying to get across is that this
E.
M.
G technique is the way in
which we recognize and
affirm that the animal model is truly
an animal model of myasthenia gravis.
In the next slide,
the same defect was seen by Dr Druckman
during immediately after and the post
titanic exhaustion observed in
a rat exposed to cobra venom
in order that one could
show that blocking of the N plate receptor
protein could produce a neuro muscular
disorder,
a neuro muscular disorder recognized by
the AMG hallmark of an early dip.
And finally in the next slide Dr
Jackman's delineation that such a
defect occurs in mice who are
given chronic administration of
immunoglobulin from patients with myasthenia
is one of the real breakthroughs and the
understanding of myasthenia gravis,
a breakthrough that supports the concept that
it is a disorder associated with
circulating antibodies to receptor
protein.
That this is clinically and electrically true
is seen once again by the early dip
phenomenon.
So much for neuro muscular transmission.
Let us move on to the next slide
at the last level of the motor unit
in muscle itself.
Various needle electrode biographic techniques
measuring conduction velocity and excitability
of of muscle fibers directly as well
are used to analyze
disease.
If we can see the theory behind these in the next
slide.
Under ordinary circumstances,
two kinds of needles are used either a
concentric needle or else
a very fine multi electrode
on occasion as well.
Single mono polar electrodes are used
and these techniques give different kinds of information.
Let us explore that now in the next slide,
schematically represented.
Here is something that anyone who has ever listened to a radio
realizes a multi electrode
placed inside of a muscle In
which only one motor unit in the center of the muscle
at level two is being activated,
will record a muscle action potential of a given
amplitude and duration above and
below.
That active motor unit the same
duration,
the same frequency,
the same tune if you were,
is heard but at much lower amplitude.
So that using concentric needles,
the duration of the motor unit is the thing that
counts book tall and his co
workers have correlated motor unit duration
with the size or the number of muscle
fibers supplied by each anterior horn cell.
And has shown that with very small motor units,
such as occur in the extra ocular muscles,
very brief motor units are
recorded and with large ones and the large muscles of the
thigh.
Long motor units are recorded.
He and his colleagues have established normal motor
unit duration values for different
subjects at different ages and in different muscles
and has shown that if one can observe
increased duration units,
then one must postulate an increase in motor
units size and again,
that can only occur when there has been
degeneration due to
neuropathy with re innovation and
increase in the size of the motor unit,
decreased motor unit duration can be
seen with decreased motor unit size
and is often referred to as my opa thicken
character.
The next slide.
Such brief motor units can be seen with
weak effort when there is spotty drop out of
muscle fibers,
whereas with whole muscle fiber drop out
and perhaps re innovation,
the motor units are larger.
There is some activity at rest in the next
slide that has a
particular and peculiar fashion.
That sounds like a motorcycle revving up for those
who remember the days of funds and
his friends on Happy Days,
the dive bomber of World
War Two.
A potential which increases in amplitude and
frequency and later decreases in
both.
In this instance,
the muscle was per cust with the needle in place
and this phenomenon is the electrical
concomitant of maya Tonia,
a phenomenon missing from a normal muscle
and a very clear and classic hallmark of the maya tonic
disorders in the next slide,
other sorts of abnormalities can be seen at
rest.
The slide was taken from dr lambert's
article in the clinical
examinations in neurology textbook from the Mayo
clinic.
Normally with insertion,
a brief bursts of potentials occurs
with no activity persisting at
rest.
If one gets right into the zone of
innovation,
miniature end plate potentials may be
recorded with the Innovation.
There are lots of
different six simple waves and occasionally
positive sharp waves as well.
The Maya tonic phenomenon we've commented on,
and a bizarre high frequency discharge can be
seen in a variety of non specified
neuro muscular disorders.
In the next slide I will review for
you motor units,
which,
if each box here represents,
10 milliseconds are seen to be quite
brief and therefore deriving from
motor units whose size
whose number of muscle fibers is reduced
in the next slide at rest from the
same muscle from which the prior slide was recorded
are seeing positive sharp waves and
fibrillation potentials.
The hallmarks largely of D
innovation.
Thus it can be seen that brief motor units
can arise when leaves,
drop off a sick rooted tree
and are not necessarily myopathy
in a path,
a demonic sense.
With that.
As a background,
one can simply relate motor unit,
size two must to motor
unit uh duration and
derive some physiologic thoughts about the
character of the problem facing you.
In the next slide
is depicted.
Another way of looking at E.
M.
G.
With increasing effort,
increased numbers of motor units are recruited
such that at maximal effort and interference pattern is
observed.
If there has been a neuropathy with drop out
of motor units,
the recruitment must perforce be
less such that at maximal effort.
Single motor units are observed
with a myopathy.
On the other hand,
since each motor unit is reduced in size,
increased numbers must be recorded per unit
effort and a more dense,
lower amplitude interference pattern and maximal
effort is seen.
There have been a variety of electronic
averaging techniques that have been used
to define the differences between these
kinds of activity and between various
points on this curve.
Suffice it to say that when one
compares these techniques to the analysis
of motor unit duration,
the motor unit duration techniques show a much
higher correlation with the ultimate clinical
diagnosis of the patient.
In the next slide,
different kinds of activity with
maximal effort are observed,
I believe these were shown schematically in the last
slide.
In the next slide,
one must recall when doing AMG studies
something which King angle showed us quite
elegantly several years ago that
inflammatory change in muscle may
occur as it did in this guinea pig muscle
within days after Needling the
muscle for electro maya graphic study.
And so the studies of E.
M.
G.
Must be done in conjunction with
examination of the whole patient and biopsy
must not be taken from an area previously
needled the next slide
because of the limitations of standard needle E.
M.
G.
Techniques,
Stalberg and his associates over the past
10 and now almost 13 years have
introduced a new way of looking at the motor unit.
That new way involves very small multi
electrodes and the
recording is made from
one or another point on the multi
electrode in response to voluntary
stimulation or in this instance,
repetitive threshold nerve stimulation.
In normal subjects 12
and often three fibers from
that region can be recorded.
And if the response to subsequent
stimuli is measured,
Each of these responses bear the
same time relationship to each other within
less than 40 milliseconds.
If we compare this in the next slide,
however,
to similar observations made in
patients with myasthenia gravis,
two things are observed in the first
instance,
the 2nd,
3rd and 4th units drop
out with repetitive stimulation
and in the second instance the timing of the second
one gets much later.
A so called jitter response
and increased duration between
the 1st and 2nd
responses is observed.
This jitter phenomenon is the
hallmark of disordered neuro muscular
transmission.
It is seen preeminently with Stalberg
single fiber AMG technique in the illness
Myasthenia gravis,
but obviously and logically can be seen in
any other disorder of peripheral nerve
or muscle in which delay in
conduction in nerve fibers or at the
neuro muscular junction or muscle fibers themselves can
occur?
I believe that's all the slides.
Is there any way we can have the slides off at this
stage of the game and simply summarize
by saying that we have attempted to review the
theoretical basis behind the
various standard clinically MG techniques,
we have indicated some of their limitations
and their application in diseases at various levels of the
motor unit,
and indicated,
I hope that if these techniques are
applied with reference to the patient's clinical
problem,
the experience will be an enjoyable one for
you,
as well as for the patient.
Thank you.