I can't remember how you were diagnosed--was it by single-fiber EMG? If so, I believe that a SFEMG can distinguish between LEMS and MG:

http://ukpmc.ac.uk/abstract/MED/1662...GECu6XFV7D.139

But the SFEMG is such as specialized test that I don't know if every neurologist who performs it can read it that carefully.

Another characteristic of LEMS is that whereas exercise makes MG symptoms immediately worse, it tends to make LEMS symptoms immediately better. But from what I read, this is one of those "sometimes" characteristics. Not every LEMS patient has this experience.

One of the first symptoms of LEMS is often a very dry mouth.

None of these things is conclusive, but taken together they might be reassuring.

I'm so happy to read that the IVIg is working for you, by the way! When I had my first course of IVIg, I also worried that I was imagining the improvement...until it started wearing off.

Abby