It is rare, but I have MG and severe hearing loss and wear hearing aids. They believe it is caused by autoimmune disease (MG). I am seronegative MG. You still have antibodies when you are seroneg, they are just ones they have yet to type and since acetylcholine is implicated....there you are. My neuro hadn't had a case of it either but it's not like MG is very common and when you add hearing loss it gets even more unlikely.