My situation is simmilar to yours, My thyroid was Hyper and the Methimezole was what brought out my MG, as soon as I started taking it things went from bad to worse fast. I did the radiation and a year later I'm just stabilized but in the end it was worth it for me!

But at that time my MG was so bad that I was willing to do anything to get my life back, I wasn't thinking long term then.