I really know nothing about this autoimmune disease but decided to do some searching .... Here is what Dr. Weil says and what he recommends. I'd bet most who deal with this have searched on the alternative therapies. Potassium seems to come up a lot in a lot of the links I've read. Prednisone comes up a lot but I know how damaging that drug is.

Myasthenia Gravis | Dr. Weil's Condition Care Guide