I'm not Alice but I'll run through this again if it's okay.
First, drugs can interfere with the SFEMG. Any steroids or other immunusuppressants. Mestinon. IVIG. Plasmapheresis.
Women's muscles fatigue more slowly than men's muscles do. This might be why women need to do exercise EMG's to show a decrement. When I had my borderline SFEMG, I walked around a lot before it.
There is the issue of "fat" being different on women than on men. There is skin, then fat and then the muscle. You know how certain things interfere with an electrical signal, like certain radio/micro-waves? Same deal with fat.
And then there's the expertise of the person doing the SFEMG.
In a SFEMG, the average "jitter" of a muscle is determined by really old studies, done like decades ago!!! So, for example, if your age is 40 and the average jitter of the frontalis/forehead muscles is 35 for your age, then they expect the jitter to go up quite a bit for it to be positive. What if your NORMAL jitter for that muscle is 15? Or what if it is 55? Then their conclusions are based on faulty assumptions.
Average is relative.
And here's a quote from one of Alice's posts on this.
Quote:
all a normal SFEMG can tell you (assuming that it was done properly and there are no technical problems, or missinterpertation such as you have reffered to among others) is that there is a normal transimission of the signal from the nerve ending to the muscle fiber.
but what if the problem is after the receptor? what if this electrical signal is not properly translated into a muscle contraction?
it is like your computer is not working properly, and a technician comes, sees that it is plugged properly into the electical socket and says to you that there should be no reason for the computer not to work properly.
there are multipe steps from the activation of the acetyl-choline-receptor to the generation of muscle contraction. and all those steps should work properly, in order for muscle contraction to occur.
very schematically-calcium goes into the cell, it then leads to the release of calcium from intracellular reservoires (this is governed by other receptors, which are activated by calcium that enters the cell, but also caffeine and other pharmacological agents), this in turn leads eventually to the "sliding" of myosin and actin, which leads to shortening of the muscle fiber. each of those steps involves multiple proteins, many of which function is poorly understood at this point. MuSK, DOK-7, Rapsyn- to name a few.
I was quite surprised to find out that the assumption that any process that leads to fatiguable weakness should also involve the acetyl-choline receptor directly or indirectly, is not based on any evidence.
to me it seems that certain "axioms" have been created over the years, which are enforced by everyone agreeing to them. or as in the "hunting of the snark" by Lewis Caroll- what ever is said thrice can't be wrong.
and most patients don't "dig" and try to understand, they just accept what they are told. I probably would have done the same, if it wasn't becoming totally ridiculous, and if I didn't have an enormous amount of "thinking time" (thanks to one of the world leading experts, who gave me treatment that totally "knocked me down", and gave a few months in which I could not do much more then think, most of the time) .
alice
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In addition, if someone has CMS, the SFEMG may not be positive at all. And if it's limb-girdle CMS, a.k.a., DOK-7, then they need to test the legs/hips. That's only one example.
And if someone has a mitochondrial disease, then they have to do a very specialized muscle biopsy to know for sure. An EMG could be completely normal.
Doctors like to have "simple" equations and solutions and science is anything but simple. Time constraints and money are often their concern and not the science of a situation. It used to be that science came first.
And that is why a clinical exam, lots of other evidence like breathing tests, a neuro-ophthalmologist exam and other evidence is so important in diagnosing a patient.
Okay, that's it for me. Alice? Anyone else?
Annie