Amyotrophic Lateral Sclerosis (ALS) FAQs
Copyright © 2002 Joe F. Jabre, M.D. All rights reserved

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Muscle Action Potential in ALS Top

Question

Hi! What is the Muscle Action Potential amplitude? Is it pathologically higher or lower than normal in ALS/Motor Neuron Disease (MND)?

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.

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 peripheral neuropathy of different etiology or revise your diagnosis to something other than ALS

Abnormal motor units in ALS Top

Question

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..)?

Answer

Fasciculations (at least Motor Neuron fasciculations) are a sign of ongoing reinnervation and can actually begin distally in regenerated nerve fibers. By the time they develop in ALS, you should see a good deal of neurogenic potentials

Comment

What do you mean by neurogenic potentials? Do you mean neurogenic units - the abnormal motor units (amplitude etc.)? Second, 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

Answer

Yes neurogenic units means polyphasic units, later on with high amplitude. In my experience, I see the neurogenic units before I see the fasciculations, or very close to them in time

Are there 2 types of fasciculations in ALS? Top

Question

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??

Answer

No, in ALS (even normal or other conditions), it is one kind of fasciculation. Clinically they refer 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. They are caused by the firing of MUPs from "irritation" in the anterior horn cells or in the entire axis along the peripheral nerve. There is no "infallible" way to tell whether the fasciculating discharge by itself is benign or malignant. The decision is made based on "what kind of company they keep". A non-progressive course is reassuring. In a study in 1993, a total of 121 patients with benign fasciculations followed up to 32 years, none developed ALS (Blexrud et al, in Ann Neurol 1993;34:622-625).

Comment

First thank you! 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 fasciculation are an early sign of ALS (as reinnervation takes place much later)

Answer

Yes, I agree that patients with ALS may present with fasciculations. 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 fasciculations occur before or after the onset of reinnervation in ALS. I do not know. However, single fiber EMG jitter studies reveal that reinnervation could be detected as early as in the fourth week after muscle transplant in healthy nerve and muscle fibers. In ALS (sick fibers), whether the process of reinnervation occurs earlier or at the same time or rate, it is not yet clear.

Interference pattern in ALS Top

Question

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 full interference pattern, however it takes much more time to reach it - is that true?

Answer

Yes, in ALS there is motor units loss, therefore, those patients have 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.

Fasciculations and ALS Top

Question

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???

Answer

It is tough to answer your first question. If you are able to see a fasciculation, you surely can pick it up by EMG recording. In fact frequently we pick up fasciculations wit the EMG needle before they become visible on the skin surface. So, unless al;l your fasciculations went away (?) on the day you had your EMG, the needle exam should have picked them up. For the second question, what you refer to are contraction fasciculations and frequently when the EMGer is looking for fasciculations and does not see them , he or she might ask you to contract your muscle to bring them out. This is not more or less problematic than their random occurrence. Finally, yes it is likely that twitching can occur for some months months without loss of strength because the reinnervation compensates for the loss of anterior horn cells in ALS and weakness will not appear until the nervous system's reinnervation capacity has been exhausted.

Thoracic paraspinals EMG Specificity in ALS Top

Question

Is that 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 neurologist 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?

Answer

If you look at the World Federation of Neurology El Escorial criteria for diagnosis of ALS; as follows: 1. Lower motor neuron signs (by clinical, electrophysiological, or neuropathological exam) in 1 or more of 4 regions (bulbar, cervical, thoracic and lumbosacral) 2. Upper motor neuron 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 an abnormal thoracic paraspinal EMG is specific for ALS, otherwise we do not need other factors to diagnose, and may have false positive diagnosis. However, let me address this point in a different way, thoracic paraspinals can be very useful muscles when cervical or lumbosacral root lesions may be present making these paraspinals less useful than the thoracic ones. Then, an abnormal EMG in the thoracic paraspinals would indicate a more widespread neurogenic involvement in favor of ALS, as thoracic root lesions are uncommon or rare on comparison to cervical or lumbosacral regions.