I have had multiple SFEMGs which were all completely normal. Most of them were done by highly experienced neruophysiologists, in the best MG centers. They were done correctly, on weak (and even extremely weak) muscles, without mestinon or any other interfering medication.

I do not have antibodies detected in the usual tests. But, was found to have MuSK antibodies using an experimental assay in Oxford.

My neurologist thinks (and I believe he is correct) that the combination of severe MG, with completely normal tests, made them question this diagnosis again and again, even though it was clinically unquestionable, and there was no possible reasonable alternative diagnosis .