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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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