False positive on emg?

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Re: False positive on emg?

Postby TwitchyDoc on November 7th, 2014, 1:52 pm

Bibi, yes, dystonia is basically a gross contraction producing aktivity similar or nearly the same as voluntary contraction (as far as the motor unit activation is concerned). I cannot go into more details as I do not do EMGs and hence have zero experience with dystonia and EMG.
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Re: False positive on emg?

Postby Pascal35 on November 7th, 2014, 6:10 pm

TwitchyDoc wrote:EMG really can produce false positives, although the probability is very low. Anyway, it would never produce findings that can be confused with MND, except for maybe some inconclusive clues that can be then incorrectly interpreted in the context of the clinical exam.

Saying that "EMG is highly subjective" is like saying that "Interpretation of the X-ray is highly subjective", it is a nonsense..While more experienced neurologist might be able to get better readings (or get them faster) due to years of practice etc., the interpretation should be the same, i.e. skill-dependant.
If there are fibrillations, positive sharp waves or other signs of abnormal electrical activity, the EMG will detect it - there is no space for any subjective judgement. It is either there or it is not, unless the doctor puts the needle somewhere else or gives you wrong instruction (like 'flex' instead of 'relax'..). Sure the interpretation is something else but in general, EMGs cannot be subjective - there is no magic in the EMG, it is a simple oscilloscope.



How can you compare an EMG with an X-ray???
X-ray is a photo that "never lies" unless the doctor totally idiot not to recognize any possible problem.
EMG is something different. There are so many inexperienced neurologists that may get confused by naming fibrillation a simple "voluntary" movement or the end plate potentials. Tell me that you never heard about it...
As i said earlier and i hope i was properly understood (english is not my mother language) - EMG is very sensitive but especially with regards to spontaneous activity or insertional activities there might be false positive mistakes. Not false negatives though. So the most important is that if you get a good results then its fine but if you get a bad one then i suggest you go and check again with another doctor. Especially if the MRI is not conclusive.
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Re: False positive on emg?

Postby TwitchyDoc on November 8th, 2014, 2:21 am

Pascal35 wrote:
TwitchyDoc wrote:EMG really can produce false positives, although the probability is very low. Anyway, it would never produce findings that can be confused with MND, except for maybe some inconclusive clues that can be then incorrectly interpreted in the context of the clinical exam.

Saying that "EMG is highly subjective" is like saying that "Interpretation of the X-ray is highly subjective", it is a nonsense..While more experienced neurologist might be able to get better readings (or get them faster) due to years of practice etc., the interpretation should be the same, i.e. skill-dependant.
If there are fibrillations, positive sharp waves or other signs of abnormal electrical activity, the EMG will detect it - there is no space for any subjective judgement. It is either there or it is not, unless the doctor puts the needle somewhere else or gives you wrong instruction (like 'flex' instead of 'relax'..). Sure the interpretation is something else but in general, EMGs cannot be subjective - there is no magic in the EMG, it is a simple oscilloscope.



How can you compare an EMG with an X-ray???
X-ray is a photo that "never lies" unless the doctor totally idiot not to recognize any possible problem.
EMG is something different. There are so many inexperienced neurologists that may get confused by naming fibrillation a simple "voluntary" movement or the end plate potentials. Tell me that you never heard about it...
As i said earlier and i hope i was properly understood (english is not my mother language) - EMG is very sensitive but especially with regards to spontaneous activity or insertional activities there might be false positive mistakes. Not false negatives though. So the most important is that if you get a good results then its fine but if you get a bad one then i suggest you go and check again with another doctor. Especially if the MRI is not conclusive.


Pascal, EMG is as objective as the X-ray, that is the point you are missing. A neurologist would have to be totally stupid to confuse fibrillations for voluntary movement (as you say), like a doctor misinterpreting an X-ray image. Sure, I have heard in US EMG are sometimes done by some kind of "technicians" which I really do not get and that might account for some cases of misinterpretation.
EMG does nothing than registering of electrophysiological activity- these signs are objective, measurable and reliable. If they were not, EMG results would be useless. Of course, some inconclusive results might not be interpreted accurately but go and ask radiologists what is their accuracy :)
As for the false negatives, funny you say they do not exist..they do. Incorrect needle placement or angle, insufficient observation time, high threshold or filter setting can all lead to readings that appear clear. That really should not happen to regular neurologists, its like messing the X-ray - it rarely happens.
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Re: False positive on emg?

Postby Pascal35 on November 8th, 2014, 5:56 am

TwitchyDoc wrote:
Pascal35 wrote:
TwitchyDoc wrote:EMG really can produce false positives, although the probability is very low. Anyway, it would never produce findings that can be confused with MND, except for maybe some inconclusive clues that can be then incorrectly interpreted in the context of the clinical exam.

Saying that "EMG is highly subjective" is like saying that "Interpretation of the X-ray is highly subjective", it is a nonsense..While more experienced neurologist might be able to get better readings (or get them faster) due to years of practice etc., the interpretation should be the same, i.e. skill-dependant.
If there are fibrillations, positive sharp waves or other signs of abnormal electrical activity, the EMG will detect it - there is no space for any subjective judgement. It is either there or it is not, unless the doctor puts the needle somewhere else or gives you wrong instruction (like 'flex' instead of 'relax'..). Sure the interpretation is something else but in general, EMGs cannot be subjective - there is no magic in the EMG, it is a simple oscilloscope.



How can you compare an EMG with an X-ray???
X-ray is a photo that "never lies" unless the doctor totally idiot not to recognize any possible problem.
EMG is something different. There are so many inexperienced neurologists that may get confused by naming fibrillation a simple "voluntary" movement or the end plate potentials. Tell me that you never heard about it...
As i said earlier and i hope i was properly understood (english is not my mother language) - EMG is very sensitive but especially with regards to spontaneous activity or insertional activities there might be false positive mistakes. Not false negatives though. So the most important is that if you get a good results then its fine but if you get a bad one then i suggest you go and check again with another doctor. Especially if the MRI is not conclusive.


Pascal, EMG is as objective as the X-ray, that is the point you are missing. A neurologist would have to be totally stupid to confuse fibrillations for voluntary movement (as you say), like a doctor misinterpreting an X-ray image. Sure, I have heard in US EMG are sometimes done by some kind of "technicians" which I really do not get and that might account for some cases of misinterpretation.
EMG does nothing than registering of electrophysiological activity- these signs are objective, measurable and reliable. If they were not, EMG results would be useless. Of course, some inconclusive results might not be interpreted accurately but go and ask radiologists what is their accuracy :)
As for the false negatives, funny you say they do not exist..they do. Incorrect needle placement or angle, insufficient observation time, high threshold or filter setting can all lead to readings that appear clear. That really should not happen to regular neurologists, its like messing the X-ray - it rarely happens.



OK TwichyDoc - As i said i am not a doctor but during this 1 year of my twitching i had over 25 EMGs in 3 different countries. Some were performed by top class high reputable neurologists and some by young and up coming neurologists. In addition i studied so much due to my fear.
Reading your response i realized that you are arguing with your own self in order to argue with me.
Firstly you argued to my original statement and you said that EMG is like an X-ray so you can't be wrong.
After my response you came back arguing with yourself saying that OK EMG could be wrong if not performed properly... I AGREE. But that doesn't make it an x-ray. It makes it a quite subjective test.
With regards to fibs and movement i am not going to insist on my earlier statement.
During my EMGs there were some muscles that while at rest there were noises. The doctors asked me to calm down until those noises went off. I believe they probably knew that this was movement and not fibs but due to my anxiety i was questioning everything.
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Re: False positive on emg?

Postby bobajojo on November 8th, 2014, 8:58 am

Pascal,
25 Emg's in one year? That's 1 every 2 weeks. im not really sure why you are arguing with Docen on this. The example you gave about noise on emg and having to relax your muscles highlights your lack of knowledge with emg testing. Most neuros when performing an emg will tell the patient to relax because the muscle needs to be still. However, the pops you hear when the muscles are not still are NOT fibrillations and would not be confused as such. This argument is silly.
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Re: False positive on emg?

Postby Pascal35 on November 8th, 2014, 12:12 pm

Bobajojo,

You are saying that these pops shouldn't be confused but I mentioned that in some cases they are confused (by inexperienced doctors) as insertional activity or fibs. Anyhow. This is not the argument.
What I do believe is that an EMG is not as objective as an X-Ray or a blood test for example. Docen disagreed with this statement in his first response but agreed in the second.
That's why i am confused.
Please don't get a wrong impression with my knowledge in EMGs and try to realize that English is not my mother language so especially in medical terms is hard to express myself.
*** 25 EMGs and honestly there were only few that worthed the stress, time and money.
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Re: False positive on emg?

Postby trustme78 on November 8th, 2014, 1:42 pm

bobajojo wrote:
Do you know what I think is uncalled for? Irresponsible statements from someone with no neurological experience that will make people wonder if their EMG was misinterpreted and keep them in the "cycle of fear" when the reality is that the EMG is extremely sensitive and accurate and if it says your fasciculations are benign, then your fasciculations are benign. So please, watch your own statements. Keep in mind that the people reading them are going through a very difficult time and are looking for reassurance. But after reading your statement, they are now going to question their EMG results.


Just want to clarify one thing: I never wanted to say that someone should question a clean EMG. I am sorry if this caused confusion and I apologize for that. Matt is right for pointing that out.
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Re: False positive on emg?

Postby TwitchyDoc on November 9th, 2014, 1:57 am

Pascal, no, I am not arguing with myself - I only wanted to give you a full view. To make it short:

Both EMG and X-Ray (or CT, MRI...) are objective tests where the results provide us with certain physiological data, independently on our opinions. As any data, this data can too be interpreted incorrectly but I as I mentioned, it would take an idiot to confuse voluntary activity for the spontaneous one on the EMG, the same way it would take an idiot to miss a clean fracture on the X-ray. The EMG can be done incorrectly with probably the same probability like the X-ray - so this is not an argument, you could then question any testing requiring human interpretation. I can assure you that the electrophysiological profile of MND is very specific - it is not just about the spontaneous activity, there are other things to consider (like recruitment pattern, F-Wave persistence etc.).
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Re: False positive on emg?

Postby Pascal35 on November 9th, 2014, 4:34 am

Thanks Twitchydoc,

That makes sense
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Re: False positive on emg?

Postby LKP1231 on November 11th, 2014, 9:04 am

I did not mean to cause trouble here. I was hoping for myself that abnormal results could be argued but I don't think they can. My test - at least the needle part was done by the nuero so I guess he must know what he's doing.
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