Blondie,
I'm also seronegative and MUSK negative. I was diagnosed with a positive tensilon test and clinical sxs, as well as some improvement with prednisone and IVIG.

I'm on Imuran currently, though having difficulty going up to a therapeutic dose without my white count dropping too low. We're giving it one more try with the Imuran, but if it drops my white count again, will probably move on to cyclosporine.

My primary sx is double vision, but I also experience both arm and leg weakness, which is sporadic. It took a long seven years to get a diagnosis. It's possible that I'm dealing with refractory MG at this point, due to the delay in treatment. I'm hoping for the best with treatment, but expect that the vision issues won't resolve and this may be the best it gets.

And, yes, the hot weather does increase my sxs, though my neurologist doesn't seem to think there is a connection.

Cate