home about us patient forums doctors forums online store contact us
Electronic EMG Manual®
Peripheral Nerves Anatomy
General Muscles Anatomy
Nerve Conduction Set-Ups
Needle EMG Anatomy Atlas
Patient Education Series (FAQ)
Nerve Entrapment Guide






  Motor Amplitude in ALS  
  What is the motor amplitude? Is it pathologically higher or lower than normal in ALS/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 neuropathy of different etiology or revise your diagnosis to something other than ALS
  Abnormal motor units in ALS  
  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 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
  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
  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
  Are there 2 types of fasciculations in ALS?  
  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 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).
  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)
  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.
  Interference pattern in ALS  
  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?
  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.
  Fasciculations and ALS  
  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 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.
  Thoracic paraspinals EMG Specificity in ALS  
  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).  
  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.
  Comment So, Isn't it true that there is some specificity for the thoracic paraspinals in ALS denervation?  
  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.

  Fibrillations and Fasciculations in ALS  
  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?  
  Answer Yes, I have seen such pattern of appearance of fibrillation first. It is however the combination of findings that is the usual pattern
  Peripheral neuropathy versus ALS/MND  
  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.)
  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.
  Motor neuropathy and ALS  
  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??)  
  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.
  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?
  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.
  The electrophysiologic diagnosis of ALS  
  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?
  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.
  Comment So do you mean that frequently ALS patients do not exhibit PSW or fibrillations in their EMG exam?  
  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.
Previous Page | Next Page
 This page was last updated on Sunday, March 04, 2012
Copyright 1997-2012 TeleEMG, LLC. All rights reserved - TeleEMG is a Massachusetts Limited Liability Company (LLC)