SFEMG - Why are they negative?
 

This topic has been annoying me for years. Why do some MG patients, who obviously have MG, have negative SFEMG's? Is it as simple as too much fat?

http://www.smpp.northwestern.edu/~sm...2005POIntl.pdf

A SFEMG needle has to go through the skin first, then subcutaneous fat and then the muscle. This article clearly shows that fat does indeed lower the frequency of the reading. I knew that this can happen when doing an EKG of the heart, so I figured it had to happen during a SFEMG. Or an RNS.

We all know about hydration, warmth of muscles, Mestinon and other drugs and things like technician experience, etc. effecting a SFEMG. But fat?

Women inherently have more fat than men. It's for a reason! ;) But what if that does indeed interfere with the SFEMG results?

I am just putting this out there in a continued effort to understand why the medical community keeps saying that the SFEMG is the "gold standard" for diagnosing MG (instead of a clinical exam and common sense and antibodies and Tensilon tests and . . . ).

Any thoughts on this? Last year I did find a bunch of information that says that men's muscles fatigue more quickly than women's do. It seems that this issue is a lot more complex than what neuros say about it. Thanks for any input or sharing your own experiences.

If we're the "weaker" sex, it sure seems a lot harder to prove it. :Poke:

Annie

This makes a great deal of sense...I'd be glad to volunteer for lipo if they wanted a test subject (hehehehe)!!

why is the SFEMG negative in patients with myasthenia?
 

The answer is very simple.

This test is much less sensitive then what it is assumed to be.

The reasons for that are not important. It could be because of a different underlying mechanism, influence of environmental factors, gender differences. The bottom line is that there are patients with maysthenia who have a completely normal test.

The very high sensitivity of nearly 100%, is based on studied with significant methodological problems.

I do not think this was done deliberately. This test seemed at the time, to solve a serious problem. It provided an objective way to diagnose an illness, that was diagnosed clinically before.

It also provided an explanation and better understanding of the mechanism of this illness.

I do think it is time to correct this error. Some neurologists understand the true limitations of this test, and some still do not.

some still think that a normal SFEMG done in a weak muscle rules out MG as the cause of this weakness even if there is no reasonable alternative explanation. Just like the top leading expert described in the book written by Chloe Atkins.

Very cute, Sue. ;)

With all due respect, Alice, the "why" does matter. And I don't believe it is a simple, one reason answer.

If researchers or doctors can figure out the reasons why someone with MG has a negative SFEMG, then maybe they can not only stop proclaiming it as a "perfect" test but can also come up with other ways to diagnose MG. Or ways to improve on how the SFEMG is done, like increasing the amplitude to counteract a "thick" layer of subcutaneous fat. Or testing muscles other than the standard EDC (forearm) or frontalis (forehead) muscles.

MG is dangerous and patients with this stupid disease need to know they have it, not be told they "possibly" or "probably" have it and then wait years to get proper treatment. Insurance companies don't authorize more treatments sometimes when you "might" have a disease. To remain undiagnosed due to a lack of information getting to doctors is one thing but this goes beyond that. The MG "experts" out there are still proclaiming this out-dated information about the test. So unless someone gives very exacting reasons why the SFEMG doesn't often come out positive, it's highly doubtful that line in the sand will be erased.

After that cosmic shift in thinking, then they can give doctors the "tools" to adapt their own thinking, depending upon each patient's individual circumstances. Of course, thinking that they'll act outside of protocols is fairly naive. They need a new, sensible protocol.

And the problem with quoting Chloe Atkin's book to any doctor is that it's written by a patient and unless an opinion is repeatedly published in JAMA, the likelihood of any doctor taking it seriously is nil. Peer pressure, as you know, is alive and well in the doctoring world. I'm afraid it's going to take a lot of people to gently push "experts" in a better direction. MG patients don't deserve to wait for this thinking to evolve.

Annie

I also think that the "average" jitters for certain age groups needs an overhaul (see attached file). There's no such thing as "average" anything, such as intelligence, physical strength, critical thinking, etc. How do they know that a jitter at age 10 isn't lower, especially if someone has had MG since birth. What if a jitter stops increasing once you get a NMJ disease?!

Erik Stalberg, the inventor of the SFEMG, isn't doing these problems any service either. Who would admit that their invention isn't what it's cracked up to be?

Annie, that would make some sense of my story. My first two SFEMGs were on my arms and legs, and they tested borderline and mildly abnormal. My third SFEMG was on my face (around my eyes), and that one was so clearly positive that it got me diagnosed (even though I'm seronegative).

The weird thing is that I have almost no eye symptoms--no double vision, no ptosis. Just a very occasional eye-strain sort of feeling.

So, could it be that the reasons is that there's no fat (or much less) in that area? I also can't neglect to mention that it was a different doctor who did the third SFEMG.

Abby

Hi, Abby. Glad you're still upright and talking. ;) Hope things are going well.

Didn't you also have the kind of SFEMG where you didn't "participate" by contracting your muscles?

Thanks, Annie! Yes, that third SFEMG, by which I was diagnosed, was a "stimulated" SFEMG. Instead of having me contract my muscles voluntarily, he had little electrodes on my face that sent out pulses of electricity (not strong ones like in an EMG--no pain) that made my muscles twitch. The doctor who did it was a neurological ophthalmologist with a special interest in MG.

Abby