Welcome, Xanadu!

When you say that all of the tests are negative, are you referring to just the blood tests, or also the single fibre EMG and repetitive nerve stimulation test(s)?

Are difficulty swallowing and breathing troubles your only symptoms of muscle weakness, or main ones?

I definately think that the abnormality of your thymus is a red-flag that MG is prolly the culprit, but it can be enlarged in some other autoimmune diseases, but has a more common affiliation with MG- plus, I'm sure that your dentist and respiratory doctor know a thing or two about a thing or two, so you have them on your side, so that's really good..

When I went to see my neuro. for the first time, I was an emotional wreck because of how bad my speech was. I was really terrified of what he was going to tell me (bulbar palsy or something). I didn't really have to do anything prior to the appointment because my symptoms occured even in the mornings and were severe...But, if I had gone 9-months earlier (I was having occasional slurred speech which I attributed to being tired, and some breathing problems which I attributed to smoking), it may not have been discovered, so I understand your fears of not getting the correct diagnosis...

I think that your symptoms and thymus speak for themselves. Lots of people with seronegative MG have an enlarged thymus with no detectable antibodies. It would be tough if the electrical tests were also negative, but it seems that it would be difficult to get a good reading if the only muscles that are affected are swallowing and breathing...I'm not sure where they'd put the needle...They put the needle on my forehead and near my lips..I have major facial weakness...

I wish you lots of luck and sorry about the long post! lol

P.S. I know that you must be scared, but this is an awesome group- lots of different perspectives, and people just like you dealing with the same issues- you're not alone!