Hi, Rose.
It's when there are 10% or greater pairs in a SFEMG that doctors consider it to be positive for MG.
http://emedicine.medscape.com/article/1832855-overview
Are your doctors thinking you have a steroid myopathy?
The irony of that kind of thinking is that Hydrocortisone IS a steroid. Steroids reduce or erase any signs of MG or other autoimmune diseases. It doesn't matter if you're on 5 mg. or 50 mg., that's what the drug does.
You could call Dr. James Howard at UNC and see if he has any consultation appointments. He's the main MG expert there. He's hard to get into to see as well. They all are.
The fact that Dr. Massey did not order the blood tests strikes me as very odd. You can't really rule out MG in your situation (due to the steroid) without extra testing.
I think that a second opinion is in order. MG is a clinical diagnosis that's backed up with tests. Maybe you don't have MG. Maybe you have an inflammatory disease. But they can't really say for sure one way or another without further investigation.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2504120/
You can't go off of that drug without serious consequences, as you well know. So the doctors are going to have to doctor outside of the algorithmic box here.
Other things you could do is to see a neuro-ophthalmologist if you have ptosis (drooping eyelids or eyebrows). Do you? Some N-Os will do the Tensilon test.
If you are short of breath, you could see a pulmonologist to assess what the possible cause of that is. MIP and MEP breathing tests would need to be done, for they are more specific to neuromuscular diseases.
Please don't get frustrated. It won't help YOU.
It was Dr. Howard who said at a conference in 2004 that it takes an average of one year for a man to be diagnosed with MG, but that it takes SEVEN for a woman to be! Sexism is alive and well in medicine. And your weight does NOT cause muscle weakness that is FATIGABLE! If you have fatigable muscle weakness, only LEMS, MG, or a CMS causes that! Duh, doctors.
So take a step back, maybe a deep breath, and take an analytical approach to getting some help. You can always scream or cry later.
We all have.
Hang in there!
Annie