I had the single fiber EMG done at the mayo clinic about my eyebrow. It came back negative so they weren't sure about MG. We re did the blookd work multiple times for the ACHR (I think thats right) just to confirm and it was abnormally high each time. The only weakness I had at the time was bulbar weakness and some eyelid weakness. That was just my experience, they tried on the the arm with no luck as well.