MK,
I'm so sorry for what you're going through. It shouldn't be up to Insurance companies to diagnose people. That's why they're in insurance, not medicine. If a neurologist has diagnosed you with MG, and they'e qualified to make such a diagnosis, the best treatment recommended for you by your diagnosing doctor should be given and covered by the insurance.
You've got a lot on your plate, and I hope that your docs. fight to get you the treatment that you need. It's bad enough that you have to deal with these debilitating symptoms, but then having to deal with this nonsense is just not fair. It seems like people are just supposed to pay into insurance to line pockets, when it's obviously our intention to protect our health in case anything ever happens, otherwise we're just paying for nothing!
I hope that it gets worked out, and you get the treatment that you need!

Nicky