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Motor
Amplitude in ALS |
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What
is the motor amplitude? Is it pathologically higher or
lower than normal in ALS/MND?
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Answer
1 |
The
motor unit potential (MUP) gets higher in MND. While the
compound muscle action potential (CMAP) is normal initially,
but in advanced disease gets lower (even absent) due to
severe loss of axons.
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Answer
2 |
SNAPS
or sensory nerve action potentials should be characteristically
normal in ALS as the disease affects the anterior horn
cell, (Amyotrophy) a motor neuron disease. If the SNAP
is abnormal consider a concomitant neuropathy of different
etiology or revise your diagnosis to something other than
ALS
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Abnormal
motor units in ALS |
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I
have read there is a connection (in ALS) between abnormal
motor units (large amplitude) and the appearance of fasciculations-
which means if there are ALS fasciculations - there will
also be abnormal units - Is that true? And if not, how
much time would it take for abnormal units to appear if
there are already ALS fasciculations? (Weeks, months..)? |
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Answer |
Fasciculations
(at least Motor Neuron fascics) are a sign of ongoing
reinnervation and can actually begin distally in regenerated
nerve fibers. By the time fascics develop in ALS, you
should see a good deal of neurogenic potentials
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Comment |
What
do you mean by neurogenic potentials? Do you mean neurogenic
units - the abnormal motor units (amplitude etc.)? Second,
so according to your answer if a person fasciculates for
months and It is due to ALS (malignant fasciculations)-
His motor units should be abnormal (huge amplitude and
so on)? How much time on average does it take from the
beginning of ALS fasciculations to the appearance of abnormal
motor units (neurogenic units)
* I am asking it because I have read that abnormal motor
units (huge amplitude.) are more common with chronic long
standing denervation |
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Answer |
Yes
neurogenic units means polyphasic units, later on with
high amplitude. In my experience, I see the neurogenic
units before I see the fascics, or very close to them
in time
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Are
there 2 types of fasciculations in ALS? |
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I
know that fasciculations in ALS are due to nerve irritation
(the same as in benign fasciculations?)- However in one
of the posts it was said that fasciculations are due to
ongoing reinnervation (the ones seen in EMG) are there
two types of fasciculations in als? |
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Answer |
No,
in ALS (even normal or other conditions), it is one kind
of fasciculation. Clinically this refers to visible twitching
of the muscle and are seen in the EMG needle examination
as fasciculation potentials. Fasciculations may mimic
normal or abnormal motor unit potentials (MUPs) as seen
in on-going reinnervation. There is no "infallible"
way to tell whether the fasciculating discharge by itself
is benign or malignant. The decision is made by what kind
of company they keep. In a study in 1993, a total of 121
patients with benign fasciculations were followed up to
32 years, none developed ALS (Blexrud et al, in Ann Neurol
1993;34:622-625).
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Comment |
Referring
to your answer: in ALS - Do you find fasciculations only
when there is on going reinnervation? Isn't it possible
to find/have them during denervation - before reinnervation
starts?
And if so, I know It is common for people with ALS to
have them as a very very early sign - does it mean that
when they feel/notice them- they are already in the reinnervation
phase (after denervation)? And if so, how come fasciculations
are an early sign of ALS (as reinnervation takes place
much later) |
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Answer |
Yes,
I agree that patients with ALS may present with fasciculation.
In one report (letter), 6.7% of ALS patients had fasciculations
as an isolated, initial manifestation of the disease (Eisen
and Stewart. Ann Neurol 1994;35:375-376). Practically,
all the patients I have seen got the fasciculation (if
present) with other signs of denervation and neurogenic
MUPs of variable degree. About your point do fascics specifically
occur before or after the onset of reinnervation in ALS,
I do not know. However, the single fiber EMG jitter reveals
that reinnervation could be detected in the fourth week
(increased jitter) after muscle transplant in healthy
nerve and muscle fibers.
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Interference
pattern in ALS |
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In
anterior horn cell disease, there is a reduced recruitment
(not full interference pattern) does it matter how long
does it take for a person to build the full interference
pattern (by increasing exertion)? Because I read somewhere
that ALS patients just cannot build the full interference
pattern, even after a lot of time because they lack these
motor units. So, FOR ALS DIAGNOSIS, does it matter how
long does it take to reach it? I mean, Is it true to say
that if a person has anterior horn cell degeneration -
he will never be able to reach a full interference pattern,
even after minutes?
*I know that in muscle fatigue, there is a full interference
pattern, however it takes much more time to reach it -
is that true? |
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Answer |
Yes, in
ALS there is motor units loss, therefore, those patients
have a reduced interference pattern or reduced recruitment.
Whatever they do, they do not reach the full recruitment
pattern. This is very much noticeable if there is significant
motor units loss. As a matter of fact this is also true
for other neuropathic conditions, for instance, peripheral
neuropathy. So, reduced recruitment is not specific for
ALS.
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Fasciculations
and ALS |
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A
couple of questions:
1) I have at least a thousand fasciculations a day. How
come during the 3 EMG's (2 partials, 1 full) no fasciculations
were detected? Seems impossible.
2) Besides random fasciculations, I frequently have fasciculations
right after moving a muscle. Is this more problematic
than a "random" fasciculation?
3) Is it likely that twitching can occur for six months
without loss of strength and still get diagnosed with
ALS??? |
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Answer |
Actually
it is not always surprising if the concept of EMG needle
recording is understood. If the tip (or the recording
pick up area) is far from fasciculating potential, then
you do not see any fasciculations on the screen. For the
second question, yes it is possible, and that is why a
follow up EMG is usually needed. Regarding time period
after onset of twitching without weakness or an abnormal
EMG, it is difficult to be absolutely precise in time.
But several months are usually acceptable by the time
fasciculation is seen, but provided no other clinical/EMG
findings.
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Thoracic
paraspinals EMG Specificity in ALS |
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Is
it true that in ALS there is a specificity of the thoracic
paraspinals and that they are almost the first ones to
show prominent denervation (PSW, fibs etc..) - my neuro
told me that if I had ALS, He would have seen that immediately
when sticking the needle there. What is your experience
in this specificity (thoracic paraspinals show denervation
FIRST and most profound one). HAVE you seen any ALS patients
who had denervation in limb muscles but had completely
clear thoracic paraspinals then (in your long experience).
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Answer |
If you look
at the WFN El Escorial criteria for diagnosis of ALS;
as follows: 1. LMN signs (by clinical, electrophysiological,
or neuropathological exam) in 1 or more of 4 regions (bulbar,
cervical, thoracic and lumbosacral) 2. UMN signs (by clinical
exam) in 1 or more of the 4 regions. AND Progression of
signs within a region and progression to involve other
regions. Therefore, from item one we cannot say that thoracic
paraspinal abnormal EMG is specific for ALS, otherwise
we do not need other factors to diagnose the disease,
and may have false positive diagnosis. However, let me
address this point in a different way, they are very useful
muscles when a cervical or lumbosacral radiculopathy is
a strong consideration, then an abnormal EMG in the thoracic
paraspinals would indicate a more widespread neurogenic
involvement in favor of ALS, as radicular thoracic lesions
are uncommon or rare by comparison to cervical or lumbosacral
lesions.
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Comment |
So, Isn't
it true that there is some specificity for the thoracic
paraspinals in ALS denervation? |
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Answer |
I too have
read about the specificity of the paraspinals, and probably
know where you saw it.
However, at the MDA clinic my EMG was overseen by well
known author, who has written some of the standard texts
on EMG and disease processes and he said this was just
a "neurological wives tale." In addition,
in one study I found on about 750 PALS, only about 50%
showed denervation in the thoracic paraspinal muscles
vs. 90%+ showing denervation in their arms.
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Fibrillations
and Fasciculations in ALS |
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In
a previous post, I brought a citation from "Cecil"
textbook of medicine which claimed that in the course
of lower motor neuron injury (ALS and related conditions),
fibrillations appear first and later fasciculations. Is
this true??? Have you seen such pattern with your ALS
(or other lower motor neuron) patients? |
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Answer |
Yes, I have
seen such pattern of appearance of fibrillation first.
It is however the combination of findings that is the
usual pattern
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Peripheral
neuropathy versus ALS/MND |
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I
know there are theoretical ways to distinguish (in EMG)
peripheral neuropathy (where there is a damage to the
peripheral nerves) and ALS (where there is a primary damage
to anterior horn cells (CNS). however I know fibs and
positive sharp waves as well as reduced recruitment are
features of both. So how is the distinction and later
the diagnosis made by EMG and NCV - How can you know where
is the source of the damage to nerves (central or peripheral)
because in both conditions there are exact signs of denervation?
* My question refers to peripheral neuropathy of the kind,
which is predominantly motor (so you cannot distinguish
by lack/presence of sensory signs) and is quite widespread.
How the distinctions are made?
I refer in my question to AXNONAL neuropathy with actual
damage to the axons (NOT demyelination where it is obvious
due to very slow velocities.) |
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Answer |
In ALS or
peripheral neuropathy the diagnosis depends on the history
and clinical presentation. Some points to differentiate:
the reflexes are brisk in ALS while they are absent in
neuropathy. In EMG, in axonal neuropathy and ALS you may
have the same findings. But the examination of sensory
nerve action potentials is important. They are normal
in ALS but they are affected in neuropathy.
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Motor
neuropathy and ALS |
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You
said that ALS and axonal neuropathy cannot be distinguished
by EMG due to similar findings but what about nerve conduction
velocity - I read that in ALS they are normal (not slowed)
aren't they ALWAYS slowed in motor axonal neuropathy?
(Is it possible to have motor neuropathy of axonal type
with normal velocities)??? The question is about the velocities
because as far as I am concerned the CMAP (amplitude of
motor nerves) is very reduced early in both conditions
so you cannot rely on that. (Correct??) |
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Answer |
Yes, the
MCV may be normal or slightly slow in either conditions
because of the low motor amplitudes in both. But the sensory
nerve response is normal in ALS but affected in neuropathy.
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Comment |
About these
distinctions you mentioned:
1. ARE THE SENSORY POTENTIALS ALWAYS ABNORMAL IN NEUROPATHIES?
ALSO IN PURELY MOTOR NEUROPATHIES (or there is not such
a thing purely motor neuropathies???) * are there any
neuropathies with motor symptoms only and motor emg abnormalities
only?
2.and what about fasciculations - are they present also
in motor neuropathies (because if not it can be one distinction)
what is the percentage of patients with motor neuropathies
who have fasciculations? |
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Answer |
Thank you.
To clarify myself, the ALS/MND require certain criteria
for diagnosis; presence of Lower Motor Neuron (LMN) findings
in at least 2 limbs, Upper Motor Neuron findings in at
least 1 limb and progression. Now, going to your point
about the SNAP, it is always normal in ALS but it may
be normal in neuropathies including motor neuropathies.
Therefore, if it is normal then it cannot be used in that
case to differentiate. About the fasciculation, it is
characteristically present in ALS but it is not the only
condition they are present in. So it is not a distinction
criterion. Last point I am not sure about the frequency
of fasciculation in motor neuropathy.
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The
electrophysiologic diagnosis of ALS |
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My
symptoms are fasciculations and minor cramps I read somewhere
that a clean EMG after 6 months of symptoms rules out
almost completely the diagnosis of ALS –
1.Does it fit with your clinical experience?
2.Is it possible in your experience that after 6 months
of fasciculation the EMG will show nothing but fasciculation
(no fibs and positive waves) but later would show ALS
(fibs and positive sharp waves or psw)
3. when you say that somebody with fasciculations has
inconclusive EMG what do you mean? Does the definition
of "inconclusive" in relation to possible diagnosis
of ALS includes actual fibrillations and psw or anything
else - what would be inconclusive in relation to a person
with fasciculations and suspected ALS? |
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Answer |
ALS
is an elimination diagnosis, that is that we only make
it after having ruled out other (and there are many) conditions
which can mimic it. Unfortunately, frequently fasciculations
have been the only thing identified with ALS. So the short
answer to your question is do not mind so much the EMG
as much as you should mind what your neurologist tells
you and if you don't think you're getting the right answers,
by all means seek a second opinion.
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Comment |
So
do you mean that frequently ALS patients do not exhibit
PSW or fibrillations in their EMG exam? |
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Answer |
No,
on the contrary, the fibs and PSW are frequently seen
in combination with fasciculation in ALS patients. If
the EMG is free from fibs and PSW it is reassuring.
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