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Evidence of Re-Innervation in EMG findings |
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In terms of reinnervation findings of EMG, including
increased recruitment, instability of MUP, increased
Amplitude of MUP (?), etc, which of these features are
reliable to predict the true re-innervation in
morphology? The reasoning process of EMG physiology is
not specific to predict morphological changes. |
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Answer 1 |
One of the first things to appear after denervation is
fibrillations and positive waves of course. Following
that (in about 2 months) the first signs of
reinnervation are an increase in the number of phases of
a motor unit, polyphasic potentials (check out:
http://www.teleEMG.com/jbr120.htm
Neurogenic Motor Unit), and increased instability of the
MUAP (high jiggle) with decreased recruitment followed
by an increase in the amplitude.
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Answer 2 |
Further comment on evidence of reinnervation in addition
to concentric EMG findings. The Fiber Density (FD)
increases after reinnervation due to collateral
sprouting. The increase of FD indicates that muscle
fibers increased for the same motor unit. The FD
therefore, is a most sensitive method to quantify
reinnervation, and therefore, the local organization of
motor unit (morphology!). Also, FD corresponds to type
grouping in pathology.
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EMG Technique (fasciculations) |
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Is there a way to distinguish between benign and
malignant fasciculations ELECTROMYOGRAPHICALLY and most
of all CLINICALLY? Is it true that rhythmic
fasciculations tend to be benign while a singular big
thumps tends to be malignant? is it true that brief
fasciculations tend to be benign. Is it true that coarse
fasciculation are usually benign while the malignant
ones are very fine ones? What of all that is true and
how it reflects in EMG. |
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Answer 1 |
This is a very common concern and generally no single
answer is satisfactory because almost every single rule
you make to define a benign versus malignant
fasciculation has an exception. Generally speaking
though I can tell you that Neurologists rely on far more
than the presence (or absence) of fasciculation
potentials to make the diagnosis of ALS. If
fasciculations become worrisome to a patient, I
generally recommend they seek a qualified neurologist's
opinion to ease their fears, because the worst thing
they can do is to self diagnose them with the disease.
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Answer 2 |
The best measure of benign versus malignant
fasciculation potentials comes from the EMG needle exam
by the company they keep...in other words... if
fibrillation potentials and positive sharp waves are
present with large motor unit potentials and polyphasic
waveforms with poor recruitment...along with
fasciculations...this would tend to suggest a more
ominous potential...A good history and physical exam is
a priority...remember an EMG exam is only an extension
of our physical examination.
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Single Fiber Amplifier Settings |
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I am having a minor debate on Amplifier settings for
SFEMG. (I believe the Filters were changed on my
system.) What are the recommended settings and have
there been any recent changes in them? Specifically, I
am concerned about the Low Frequency Filter Setting.
What would be the upper limit? What is the typical
setting? |
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Answer |
The
recommended or typical filter settings are LFF 500 Hz
and HFF 10 KHz. I may use LFF 1KHz (narrower settings).
This LFF setting would reduce the disturbing distant
muscle fibers. This setting, however, affects the shape
of the single fiber potential. But it should not affect
the jitter value or fiber density reading. I am not
aware of recent changes. However, if detailed
measurement is needed for the shape of action potential,
then use more open filter settings LFF 2 Hz and HFF 20
KHz.
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Theoretical guidelines vs. practical for thoroughness of
EMG studies |
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Having read the guidelines in the online EMG manual for
the thoroughness of the study of a muscle (i.e. testing
20-25 units for both spontaneous and voluntary activity,
calculating average amplitude phase etc.) I am curious
why it seems these guidelines aren't followed more
often. Having had a number of EMGs in the past year in
both local and university settings and in all cases only
3-4 units (1 insertion 3-4 directions) was sampled. One
of these EMGs was overseen by a very renowned name in
Electromyography (no names, but odds are you have one of
his books on your shelf,) and even then 1 needle
insertion per muscle. In a dialog with a doctor who does
follow these guidelines, I was told many of the patients
he performs EMG on tell him that his study is far more
thorough than that done by their own neurologist. I
fully understand the reasoning behind the 20-25 MUP
guideline if for no other reason than to increase
diagnostic accuracy. My questions then are twofold. Do
most Electromyographers routinely follow these
guidelines or are they followed only when the
situation/case dictates. Secondly, how much diagnostic
accuracy is there when only 3-4 units per muscle are
tested, for example during a MND workup, and no
abnormalities are found? |
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Answer |
I agree not all EMGers follow these guidelines, although
I do catch myself sampling less frequently in follow-up
studies when I am only looking for changes.
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Comment |
My EMGs have been done locally. I certainly understand
your comment about less stringent testing when verifying
a change. My main concern is with initial testing where
the results are negative, no sign of any disease
process. With what degree of certainty can the
electromyographer state that the muscle tested is normal
when only testing 3-4 units in that muscle? Are they any
statistics or figures on how the number of units sampled
in a muscle corresponds to diagnostic accuracy rates? I
can calculate numbers based on basic probability theory
but was curious if any formal studies or accepted
statistics existed. Thanks again and kind regards.
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Answer |
Tough question to answer. I don't know of any studies of
predictive statistics (for the number of muscles tested
vs. diagnostic accuracy rate) That would be an
interesting study. As for number of units tested,
naturally if you find the abnormality in the muscle
early on (with 3-4 units), you don't need to go any
further. But if you don't, the general rule of thumb is
to be more thorough to increase your chances.
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Answer 2 |
I agree it would be an interesting study. From a
strictly mathematical perspective it should be fairly
easy to compute the "odds" of finding abnormalities.
This is a lot like the classic probability problem of
given that a person throwing darts can hit the bulls eye
x% of the time, how many times must they throw the dart
to have a given percent chance of getting a bulls eye.
In the case of EMG the "x" can be the percentage of
units in the muscle involved in the disease process. The
number of throws would be the number of units tested and
percent chance of getting a bulls eye would correspond
to the odds of hitting an involved unit. The equation
for this would be: ln(a) = ( ln(i)) / (n)) In this
equation the variables are: a - the percent chance of
hitting an involved unit expressed as a decimal (i.e.
56% = .56) i - the percentage of units in the muscle
involved in the disease process as a decimal n - the
number of units sampled in the muscle I have made
several assumptions in this equation. 1. The involved
units are randomly distributed throughout the muscle. 2.
When the needle hits an involved fiber, the pathological
signs such as fibs, positive waves, polyphasic units
etc. will be visible to the EMGer. 3. The insertion
points will be randomly distributed across the muscle.
This is not entirely accurate since there would probably
only be 4-5 actual insertions through the skin and then
testing in multiple directions to get the 20 units.
However assuming the insertions were not all done in the
same spot, the equation holds. The results of this
calculation clearly show why sampling more units can
yield more accurate results. Examples: Sampling 20 units
in a muscle with 10% involvement gives you a 90% chance
of finding an involved unit Sampling 4 units in a muscle
with 10% involvement gives you a 56% chance of finding
an involved unit. Sampling 20 units in a muscle with 25%
involvement gives you a 93% chance of finding an
involved unit. Sampling 4 units in a muscle with 25%
involvement gives you a 70% chance of finding an
involved unit. Sampling 20 units in a muscle with 50%
involvement gives you a 97% chance of finding an
involved unit. Sampling 4 units in a muscle with 50%
involvement gives you an 84% chance of finding an
involved unit. So sampling more units in a muscle
greatly increases the chances of finding an involved
unit, especially early in the disease process. Kind
regards
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Answer 3 |
I read the interesting discussion on this point. I
believe that few additional factors may influence the
number of motor unit tested. Firstly, the experience of
the neurologist or electromyographer. Secondly, the
clinical examination of the patient. And finally, the
degree of patient's cooperation during sampling. It is
also, basically, the same argument could be applied to
the number of F-waves should be obtained for shortest
latency. My kind regards,
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Answer 4 |
Very interesting subject. About 4 years ago I was in
Italy / Milano/. At the very famous S.R. Hospital I saw
the following practice. The electromyographer there does
not catch even one potential at single muscle. They say
to the patient to do a slight effort, then observe
moving potentials (do not record), after e period of few
minutes they made conclusions e.g. MUP with growth of
amplitude and area. I asked them how long of a period is
needed to become proficient in this method: - 3 months |
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Single proximal conduction block, significance? |
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How significant should a single or isolated motor nerve
proximal conduction block be as diagnostic sign, for
instance in multifocal motor neuropathy, inflammatory
demyelinating polyneuropathy or the "new entity" the
multifocal inflammatory demyelinating neuropathy.
Occasionally, I come across such an isolated finding,
rechecked to exclude technical. |
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Answer |
No single
"isolated" abnormality should be diagnostic for a
specific lesion. What is the waveform morphology?
Abnormal temporal dispersion is usually absent in MMN.
"Inching" along the course of the nerve often can
demonstrate if the CMAP diminishes abruptly as in MMN,
or progressively as in chronic axonal loss or
demyelination. What clinical signs are present upon
examination? Asymmetric distal weakness generally is
present in MMN versus symmetric, proximal weakness in
CIDP. The presence of a single proximal conduction block
across common sites of entrapment is not helpful in
establishing a diagnosis of MMN.
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NCV “latency” |
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The Latency that is measured: 1.Does it depend on the
distance taken by the examiner? 2.Does it depend on the
amount of electric stimulation (such as the CMAP
amplitude)? 3.Is it better when high or low? |
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Answer |
Yes, the
latency depends on the distance, the greater the
distance, the longer the impulse has to travel and the
greater the latency. It also depends on the amount of
electricity you use; if you are submaximal, you are not
stimulating all the fibers and your measurement will be
inaccurate. That's why in nerve conduction it is advised
that you use supramaximal stimulation which is maximal
stimulation + 25% over that to ensure stimulation of all
the nerve fibers.
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Timing of benign vs. pathological fasciculations |
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One small question, in your electronic EMG manual you
state that benign fasciculations generally occur at
8-second intervals whereas pathological ones occur at a
slower rate of 3.5 seconds. In another online resource
that has video files of EMG findings:
http://www.med.ohio-state.edu/physmed/videos/EMGvideos.html
They say the opposite, "Non-pathologic fasciculations
usually recur at a very slow rate (less than 3 per 10
seconds), while pathologic fasciculations most commonly
occur more frequently than 3/10sec." While I know that
without other EMG findings (or lack of) it is tough to
say one way or the other if fasciculations are good or
bad but I am curious about these different viewpoints.
Thanks again for providing such a valuable resource! |
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Answer |
I am aware of the discrepancy in the literature on
benign vs. malignant fasciculations. Over the years, I
find myself no longer regarding this as black and white
but rather find myself relying more heavily on many
factors such as the shape of the fasciculation potential
their distribution and what else I am finding. For
instance, the more complex and "polyphasic" the
morphology, the more likely I am to consider them
pathological (I don't like the term "malignant"). Other
factors that enter my mind is their widespread
distribution and the presence of other signs of ALS such
as fibs and positive waves and neurogenic units. So I
now rely on the "environment" in which I find the
fasciculations rather than on one or two factors alone.
Thanks for your kind words.
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Comment |
Thanks for the reply. I understand your point about what
else you find being the true diagnostic criteria. I am
curious though which theory is "supposed" to be correct
or is there no real consensus?
Also if it isn't too complex what is the reasoning
behind one being "slow" and one being "faster?"
Again thanks for taking the time to help not only me but
all the people who come here with questions. With kind
regards, |
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Computer assisted EMG! |
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I know that some of the neurologists use computer
program for the analysis of EMG needle insertion
results. However, I am not sure how advanced these
computer programs are! In my EMG exam I got the results
within minutes after it ended (normal) and the
neurologist told me that his computer program makes much
of the analysis for him rapidly - for example MOTOR UNIT
ANALYSIS! He said this advanced program analyzes the
motor units! MY QUESTIONS ARE: 1.Does it sound possible
(motor unit analysis done by a computer program? 2. some
of the results of a muscle were (motor unit) (tibialis
anterior) AMP (normal), Duration (normal), poly (normal)
STABILITY (normal) INTERFERENCE PATTERN (normal) Is
there any computer program that can analyze these
features of MUP "alone" - I mean check these MUPS
features for the neurologist without he analyzing it by
himself? MY question refers mainly to motor unit
stability (but also AMP, duration, IP and poly) - can
the computer check if the MUAPs are STABLE without the
neuro "doing this job", can the computer tell by
"itself" the motor units are stable and not polyphasic? |
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Answer 1 |
It is amazing what computers can do. I think we have not
seen anything yet, still more to happen in the future. I
can recall an American association of EMG and
Electrodiagnosis session in 1984 about role of computers
in EMG by Joe Jabre and David Hampton. The Computer
program was able from that time to perform MUP parameter
analysis. The software is getting better. The point that
the computer is willing to help but I think working
experienced human brain is always needed to rectify the
technical problems, for instance, quite frequently you
need to correct the position of markers during MUP
analysis otherwise you may end up having false prolonged
polyphasic unstable MUP.
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Answer 2 |
Thanks for this interesting question! The truth is
computers have come a long way since the early 80's and
can "assist" EMGers a great deal but not make diagnosis.
There are still a lot of things that an experienced
EMGer can pick up that can be missed by the computer.
More importantly if the recording electrode is not
placed in the appropriate area of the muscle, you feed
poor quality data to the computer and as the saying goes
"garbage in, garbage out". So yes computers can be very
helpful but no they are not smart enough to replace
humans.yet. |
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Comment |
I know computerized EMG is of great value! Your insight
on this fascinating use of computers will be highly
appreciated! My question is: (using the most
sophisticated computer programs) - does the computer
calculates and prints out specific answers or just
"normal"/"abnormal" - for example MUAP A. Stability -
does its output is: "normal stability"/ "reduced
stability",/"slightly reduced" or just "abnormal
stability". And for B. amplitude and duration - can the
computer calculate them and "decide" by its own -
whether these are within normal ranges? C. And what
about the IP - can it "distinguish" several levels of
reduced IP or it can just decide "normal/abnormal"? * I
would appreciate your insight on these 3 features of the
computer analysis (stability,amp-dur and IP) * when It
does this MUPS analysis by "ITS OWN" how many motor
units does it check (10,20,30,40) How much time does it
take for it to check this number of MUAPs (seconds???)
THANK YOU FOR READING THIS AND I WOULD APPRECIATE YOUR
INSIGHT! |
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Answer 1 |
Yes the computer does all those functions, but of course
with manual help i.e. operator should accept/reject the
potentials. The system can take any number of MUPs, the
operator should again decide that number. |
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Answer 2 |
This is a very general question as you can gather and
different machines have different programs for different
tests so it is impossible to answer this in a
"wholesale" fashion. However, as far as motor unit
analysis is concerned, most programs used usually give
printouts of measures (numbers) for amplitude, duration
and number of phases and some do firing rate analysis.
Some do Turns and Amplitudes analysis. Some of these
numbers are generated as numbers and some are plotted
against a "cloud" of normal reference values and those,
which fall outside the cloud, are called abnormal.
Generally speaking, and realistically, only 5-6
different motor units can be properly analyzed from one
needle location, because, as more motor units are
recruited, the tracing becomes too complex for the
program to analyze and the data generated less reliable.
Most programs today on commercially available equipment
can reasonably follow a contraction up to 30% of maximum
and after that they become unreliable. To do a
reasonable computerized motor unit analysis, it usually
takes anywhere between 30-45" or up to a minute per
insertion.
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Comment |
It was pleasure for me to have your insight on the
computer assisted EMG issue. You said you do not know
what program did he use: well, He said this "is the most
sophisticated EMG program and that it is able to do mups
analysis almost alone!
Yet; another question. What about positive waves and
fibrillations- Is the program capable of detecting
(distinguish them from other activity) and count them
and at last print How many of them there were? (I think
HE said it can)
The output of the computer was: (all the insertions)
fibs -0/10 PSW- 0/10
What DO these numbers mean? Is there any computer, which
can pick up fibs/PSW by its own, distinguish them, count
them and print their number without the examiner doing
that? |
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Answer |
Sorry, I cannot comment on all the specifics as these
vary greatly from system to system and EMGer to EMGer |
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Comment |
My question is again about the use of computers in a
regular EMG test. Is there any computer program nowadays
that can pick up fibrillations, count them and
distinguish each one of them by its own. And then output
for example: "3 fibrillations"? I know that each
fibrillation has its own rhythm so that is why I am
asking if there is ANY computer program that is able of
distinguishing each one of them and of course,
recognizing a fibrillation and distinguishing it from
any other activity and all by its own?????? (MY main
question is about the ability of any computer program to
identify and recognize a fibrillation and distinguish it
from any activity) |
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Answer 1 |
In the ones I am familiar with it is the doctor that
picks the number of fibrillations he or she sees in the
muscle and enters them into a report generation software
in the computer which then prints it |
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Answer 2 |
Although there is none at present time but it sounds
like a potentially possible idea to make a computer
program to do such fibrillation and PSW detection and
counting, similar to spike detection in EEG. Perhaps, it
is a matter of time |
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EMG “Interference & recruitment” |
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What about the interference pattern and motor units
recruitment?? Is There any computer programs that can
"decide"" if the IP was full? What is the output
normal/abnormal or it can also distinguish different
levels of poor recruitment?? and motor unit stability?
What is the output in this case? (stable/unstable or
various degrees)? * In my EMG the neurologist told me
the computer does mups analysis all by its self within
less than a minute per insertion The results were:
"stability: normal, IP: normal" and he told me his new
computer program can decide and check these two
parameters by its own. Is it possible (regarding these
two parameters)? And what would be the output (the
question above) |
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Answer |
Again not knowing the specifics I can only answer this
question in general terms:
The IP is (usually) studied with a program called the
Turns and Amplitudes analysis. This is pretty rapid and
can give an idea of the interference pattern. It usually
plots the data inside a normal population cloud. If your
data is inside the cloud the IP is OK, if it's outside
it is not. So the output here is graphic.
Stability is decided upon by what is called a
"jitter" between the various components of the motor
units, and again, since motor units are only adequately
analyzed at a 30% level of maximum, only those which
could be appropriately analyzed can be called stable or
unstable. So the output here essentially is text
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60 Hz Electric interference |
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When putting the needle (in my EMG) in left triceps,
there was a very steady wavy line instead of the normal
straight normal line my neurologist just could not reach
the desirable wavy line. (I think there was not any
sound) - during voluntary activity everything was
normal. IT was a steady ("sine like" or "snake like"
wave) - I think It was not fibs- because there was no
sound and fibs look more like spikes - mine were very
very wide "tall", "fat" regular steady waves. They were
upward negative (thus, not PSW). And it was so steady. I
think I recall He said It was nothing pathological, but
an electric disturbance from the background. Does my
description sound like such known electric disturbance
from the background? What else could it be? And if it is
an electric disturbance from the background - Does it
have ANYTHING to do with the condition of one's muscle
(poorly relaxed for example) because it was normal
straight line in the right triceps. |
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Answer |
What you describe sounds like pure 60 Hz interference
from nearby devices or a poorly attached ground. None of
that is pathological, just electrical artifact.
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Can EMG test flexibility? |
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Could anyone advice me if EMG can test flexibility and
if so are there any references you could give me. |
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Answer 1 |
Certainly the muscle flexibility is important in sports
and athletics. It generally would reduce injuries. In
"routine" or the conventional EMG, we do not measure or
test for muscle flexibility.
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Answer 2 |
Routine EMGs cannot assess the flexibility of the
muscles rather it is only a diagnostic tool. Flexibility
is best measured clinically. |
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