EMG Results?

[curtis]

Hello Doctor:

I am a 38 year old male who has been having some disturbing symptoms over the last nine months.  I began having fasciculations over most of my body in May of 1999 but they seemed to mostly be in my calves and feet.  In June my neurologist and I noticed some mild atrophy of my right foot.  An EMG was normal except for a slightly slowed velocity of my right tibial nerve (40.6 vs a normal of >41).  All amplitudes were normal.  In October I began having a strange "dull" sensation in my left arm and things also began feeling heavier in that arm.  In November I had another EMG on that arm which was normal.  The sensation soon went away but the "weakness" and fasiculations  remained.  In January, the sensation returned along with some mild transiant dexterity problems in my left hand.  I just recently had another EMG which unfortunatlly showed a rather dramatic drop of amplitude of my left median nerve (13 down to 4). The signal was also "dispersed".  The needle exam was normal (including no fibs or fasics) except for some mild "myopathic changes" in my left deltoid and flexor carpi ulnaris muscles (decreased size, duration; increased frequency). By the way, my right tibial nerve was normal.

I am somewhat concerned about ALS. My grandfather died of it while he was in his late fifties.  Two seperate neurologist do not think I have ALS but cannot give me an explanation for my problems.

My questions are as follows:

1. What can cause a quick and dramatic drop of amplitude and can you experience fasiculations and weakness before anything bad shows up on an EMG (such as a drop in amplitude)?

2.  Can you have atrophy and still have a normal EMG?

3.  Can famial ALS miss one generation and then hit the next?

4.  If you have a low amplitude that is causing weakness and fasiculations, shouldn't something be seen on the needle exam?

5.  If you are having weakness and fasiculations due to ALS, shouldn't you also be seeing fibulations or do they tend to appear later?

Thank you very much for this great service and I look forward to your response.

Curtis

[rk]

You can infer the meaning from the previous sentence, "Low amplitude means that the electricity or conduction flowing down the nerve is not correct or there is demyelination occuring."  If the conduction flowing down the nerver is not correct you can infer he meant the needle exam would be normal, but the conduction velocity would be abnormal (as it is not flowing down the nerve correctly).

[curtis]

Thank you for your help, but I am just a little confused about one of your answers.  With regard to low amplitude, in your second to last paragraph you say: "Here, the needle exam would be normal, but the conduction velocity would be normal." Should they both be normal or just one of them?  Thanks.
Curtis

[Dana]

What's the difference between fibrillations and fasciculations?

[CCF Neuro[P] MD, RPS]

Dear Curtis:

There are certain criteria for ALS using EMG and ones needs three different muscle groups to show fasciculations and fibrillations.  Clearly, you do not fit the standard criteria.  Second, you did not mention the presents of fibrillations, which must be present for a diagnosis.  Third, your neurological exam, although you feel weakness, did not show objective weakness, another indication that you do not have ALS.  Fourth, you do not have both upper and lower motor neuron signs, also suggesting that you do not have ALS.  After 9 months of symptoms, you should likely show more signs of ALS if you had ALS.  Based on these things, I would agree with you neurologist that you likely do not have ALS.  The hereditary form of ALS would not skip a generation, it is not a dominant trait and this form is so rare, (only 10% of ALS is hereditary) that it would not skip a generation and find you.  Base on this you do not have the hereditary form of ALS.  

The answer to your first question is yes, but for different reasons.  If you had Guillian Barre, the EMG would initially be normal with profound weakness.  However, the weakness is clearly evident on neurological exam, which you definitely did not have.  Usually, with fasciculations and fibrillations, the EMG is clearly positive.  

No, you cannot have atrophy due to a peripheral cause and have a normal EMG (at least that I am aware of).

If you have muscle weakness that is clearly evident on neurological exam, you should have a positive needle exam.  Low amplitude means that the electricity or conduction flowing down the nerve is not correct or there is demyelination occuring.  Here, the needle exam would be normal, but the conduction velocity would be normal.  This is what you would see in early carpal tunnel.  

The answer to your fifth question is yes, if you had ALS you should be seeing fibrillation with your fasciculations.

I hope that I have helped you some.

CCF Neuro MD