FALSE POSTIVE EMG TEST

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FALSE POSTIVE EMG TEST

Postby Bradford on August 18th, 2004, 2:17 am

I've been away for a couple of months and have recently revisted the site.
I spent some time reading and responding to different posts and generally find this site informative and mildly entertaining.

I just finished reading a thread where a member responded about the dangers of having too many repeated tests (e.g. EMG/NCS) because of false postive readings. For some reason this seems more statistically based than it is actually occuring.

When one consideres the nature of the needle exam and how it evaluates the muscle at rest and during a contraction, the idea of a false postive is less likely to occur when all levels of the test are weighed in and considered.

For example, the test may find fibrillations, but when recruitment is checked during contraction, it may be normal. That is motor unit amplitude is normal and recruitment shows typical interference patterns.
These two results are not consitent with each other. One indicates nerve degeneration while the other shows perfect nerve/muscle function.
It doesn't take a rocket scientist to figure out that 2+2 isn't adding up to 4!

This is not a false positve test but rather pure error. If the EMG/NCS was simply a single level test, then false positives may likely occur with frequecny and reputition, but because it is a multi-functional test, an error or false positive can be quickly evaluated against additional findings and checked to see if the various findings are consistent.

A false postive EMG/NCS would mean that ALL aspects of the exam were consitent with abnormal results leading the physican to think that the patient has something wrong. Not only that, the physician must weigh in on the physical exam. I would think that a normal motor exam with perfectly normal reflexes and no sign of Babinski response would be
contradictory to an EMG/NCS study showing fibrillations, increased motor unit amplitude and abnormal recruitment patterns.

I can't argue that false positve results don't happen, but I can argue that an experienced physician can quickly and easily identify false positive results when they occur. In this case repeating the test would be a good idea.

To conclude, physicians stop the needle exam when they feel further insertion points are not relavent or expected to show different results than previous insertion points. A false positive reading would typically stand out and generally the first insertion point is revealing enough for abnormalities.

If false postive results occur with frequency in the EMG/NCS study, the test wouldn't be reliable diagnostic tool. I also find it very difficult that physicians would even consider and be authorized to doing multiple repeated tests unless there were abnormal findings.

My question is then what really is a false positive EMG test?
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Postby jcavan4125 on August 18th, 2004, 12:49 pm

Hi Bradford,

Welcome back. I agree with everything you said, but I do see several potential areas where you can get false readings on EMG. Now, I'm not saying that they are all likely, just a potential issue.

Whenever you are dealing with a test there are several different oportunites for error to creep in. With regard to EMGs, I see the following.

1) The physical location of the test: If the ambient temperature of the room is too low you can have false positive readings. Cold muscles react diferently than muscle at normal room temperatures (70 degrees and above). An example of how this could happen would be... it's Montana in December (it's ten below outside). You arrive at the location for your EMG and the heat is out. The technician decides to do the test anyway.

2) The machine itself: The calibration is off or there is a short in the wiring causing interference in the signal or there is a problem with the software.

3) The subject being tested: He/ she is anxious (which may cause increased muscle excitation); this may lead to abnormal insertion readings when the needle is inserted to various areas. As mentioned above, cold muscle might also act this way. Another issue would be if the subject did not give proper effort when asked to flex the muscle or push against a resistance.

4) The technician doing the testing: inexperience or carelessness could lead to inaccurate data capture.

5) Transcriptionist: the possibiltiy of inaccurate data transcription. Happens all the time in both medical and legal transcription.

6) Neurologist: The possibiltiy of over-reading or under-reading the data presented.
Joe... "That which does not kill us makes us stronger"! - Nietzsche
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Re: False Positive reading

Postby Bradford on September 22nd, 2004, 8:05 pm

Hi Joe,

I agree with your assesment about the potential for error. Number one
on my list would be in-experienced technician. I'm thankful that my
neurologist was a board cerfitified electgromyographer and did not use
a technician to take data.

In my line of work when I do field testing and it "feels" wrong, I can usually work back and pin point something that I did or at least suspect something that led to things not correlating. A neurologist doesn't have that luxery when a technician is used.

The more chefs that are in the kiitchen, the more likely that chicken will become fish on the menu. For what its worth, I had a second opinion last month from UCSF and everything is great. After putting my condition to rest, my fasics have be on the decline I'm happy to say.

Now that I've lived through probably the most stressful period in my life to date, I can say with confidence that stress and anxiety does make a huge difference with BFS. Hope you are doing well!

Brad
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Postby amy_twitch on September 23rd, 2004, 12:07 pm

I have to wonder about 'false positives' with the EMG too. What does false positve mean? A false positive reading is much different and far less significant than a false positive diagnosis.

If the person performing the EMG found any abnormality, they'd be double checking right away and/or sending the patient for further evaluation. These people are qualified, and they wouldn't allow uncertainties to just linger.

I agree that the more tests you have, the more likely you are to find 'something' wrong. My GP frowns upon people going out and getting the 'total body scan' when it's not ordered by a physician. She said often times these scans will pick up on a benign cyst somewhere in the body, and it works the patient up into a frenzy...etc... This makes sense to me.

Back to the EMG though---I just don't see what a 'false positive' would mean. I'd like to see the statistics of someone being 'falsely' diagnosed with something like ALS from an EMG.

Yes, theoretically the EMG might pick up false abnormalities (for the reasons Joe mentioned)--but those would then be confirmed or denied through further or repeat testing, right?

Point being: I guess I can imagine that an EMG might falsely pick up on some type of abnormality. But further testing would be done before any diagnosis is rendered. When it comes to TRUE DIAGNOSIS (which is made by the doctor--not the EMG machine), the false positive notion (with respect to the EMG) is very unlikely.
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Postby jcavan4125 on September 23rd, 2004, 3:31 pm

I do agree with you Amy. That's why it is so important for physicians to interpet the results of the test and ask themselves,.. "what does it mean, and what does it mean in this case".
Joe... "That which does not kill us makes us stronger"! - Nietzsche
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Postby Alien Host on August 23rd, 2005, 11:14 pm

This is an interesting post that I thought I would bring back up.
I am hoping that this is what happened to me..
I was freezing cold when I got mine done. And I know I didn't use full force because I was scared to hurt my Neurologist, or break the needle off.
Anyone have anything to add ?
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Postby Pole on August 24th, 2005, 2:45 am

Alien Host wrote:I was freezing cold when I got mine done


Temperature has an important meaning only for nerve conduction study...not for needle examination

Alien Host wrote:And I know I didn't use full force because I was scared to hurt my Neurologist, or break the needle off.


It wasn't smart. You should use all your power when your neurologist told you to do that. It could change some result (recruitment, MUP), but have nothing to do with your fibs and PSW findings - those are findings in rest.

regards
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Postby migolivas on August 24th, 2005, 11:21 am

Another problem is that (although rare) some healthy people do have fibrillations. In fact, one neuro that administered an EMG to my father said he personally has had them for more than ten years, but has never had any other symptoms of ALS.
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Postby basso on August 24th, 2005, 12:42 pm

I posted this on another thread but it seemed to get lost in a sudden burst of other postings, which I am sure were important as many of them were directed towards people with immediate concerns. I hope you do not mind me re-posting on this thread as I feel that it is relevant.

There have been a number of movies that have explored what could happen if machines began to dominate humans. They always start out with the machine/computer being friendly and benign, and end up with the technology controlling in an evil way. In the movies they make it obvious for us to tell between right and wrong, if you will. However, things in life are seldom that clear. Why? I think it is because we humans rationalize this, that and the other in order to justify living lives that are incomplete. We know this instinctively but yet we insist on creating realness, rather than being real.

It is for this reason that I do not believe in technology per se. I can see what it can do, which is oft times helpful, but I can also see it's limitations.
An EMG or MRI is just a test, a machine with a human behind it. It is nothing more, nothing less. If we look to it to validate our health, or lack thereof, than we will feel no respite from our dread. Science in all it's glory can still not say why a flower grows. To reduce our health down to the deduction of a machine, and an interpretation of that machine is a dubious practice.

I am not against machines, science or tests. What I am against is using them as a substitute for our common........sense, as a replacement for our faith in ourselves and in the incredible vitality of life itself. Most people are not stricken with a dreadful disorder when they are relatively young, is this not incredible, should this not form the cornerstone of our belief system?

There is within all of us a deep well of understanding, a light that shows us the way. If that were not true then how could we survive the millenia? What kind of healing or healer are we looking for? Someone who pricks and prods and then makes a pronouncement based on electronic squiggles.
Technology is just a tool, and it's a good tool. but it should not be the only tool in our toolbox. There is also critical thinking, horse sense, love, passion, compassion, understanding, and faith.

We twitch, what of it? It is not in the defining of that twitch which leads to succour, to wellness, but instead in the understanding of the condition/s which led up to that. The canvas that comprises a life is vibrant in colour, and rich in nuance. Machines can make false-positives/negatives and maybe positive/negative falsehoods but one thing is for CERTAIN: a life is not false, and should not be reduced to the dictates or whims of a test, a machine.

Cheers,
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Postby Bless_You_All on August 24th, 2005, 1:02 pm

I'm sorry to say that there seems to be a lot of misinformation here :

Bradford wrote :

For example, the test may find fibrillations, but when recruitment is checked during contraction, it may be normal. That is motor unit amplitude is normal and recruitment shows typical interference patterns.
These two results are not consitent with each other. One indicates nerve degeneration while the other shows perfect nerve/muscle function.
It doesn't take a rocket scientist to figure out that 2+2 isn't adding up to 4!


Not true !!!
One is a sign of active denervation (fibs. and PSWs) and the other (large MUPs and/or red. recrutiment) a sign of chronic denervation. Active usually preceeds chronic (and usually there along with chronic once the chronic stage starts). High insertional activity can be the earliest sign of denvervation (but it may not be).


Pole wrote :

Alien Host wrote:
And I know I didn't use full force because I was scared to hurt my Neurologist, or break the needle off.


It wasn't smart. You should use all your power when your neurologist told you to do that. It could change some result (recruitment, MUP), but have nothing to do with your fibs and PSW findings - those are findings in rest.


Not True again !!!
Reduced effort makes a difference to Interference patterns only (that they will not be complete). Interference patterns are non diagnostic by themselves. They do a turns per amplitude or other types of analysis and based on the "effort" AND "interference patterns" they calculate recruitement (it is an objective finding). The large MUPs will NOT come due to reduced effort.
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Postby Bless_You_All on August 24th, 2005, 1:42 pm

Doug,

Find out if your report says reduced for only the interference patterns or the recruitment also. They are two different things. Also, was the duration and/or amplitude increased or was it normal ?

I know your case and if you say the recruitment was reduced then I'd have to say that if 3 Neuros at respectable centers did not find weakness, it is a questionable finding. If you say that only interference pattern was reduced but recruitment was normal then you should blow it off.

Regards.
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Postby Schuey on August 24th, 2005, 1:46 pm

Basso, I agree with you, I think we have to apply a good dose of common sense as well. And by the way, I'm sure my vaccum cleaner has secret plans to take over my house!
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Postby Alien Host on August 24th, 2005, 2:32 pm

Bless_You_All
I actually did not ever get to see the report. In fact, when I was at Cleveland Clinic it was not in the file my Community Neuro had prepared for me to take along. We called in and the two Neuros talked about it over the phone. It just so happens that the EMG report was never dictated and put in my file. (why?) I did hear the CC Neuro repeat some things back. Fibs, Sharp waves, Radiculopathy.. I think he did say something about or asked about reduced recruitment. When I asked him what all that meant he just said it means nothing right now because the physical exam does not match the data. This is all very technical but I think I understand a little bit more now. Does the IP depend more on firing rate and the recruitment depend on how many MUAP's?
Thanks ...

And about those machines taking over....
well guys.. I think it is a matter of time before we are all jobless. Even at the highest ranks. Can you imagine that one day that the President and other Leaders could be replaced by software..
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