First of all, keep in mind that I am unable to diagnose you because I am unable to examine you, this forum is for educational purposes.
Myastenia Gravis (MG) is caused by an immune reaction to the components of the neuro-muscular junction. This immune response stops effective delivery of acetyl-choline (the neuro transmitter) to muscles cells and thus causes weakness. The most common forms of MG involve immune response in the form of antibodies to the acetyl-choline receptors (binding, blocking and modulating). If these antibodies are negative the patient is called 'seronegative', and were initially a mystery. Antibodies against MUscle Specific Tyrosine Kinase (MUSK) were also discovered to cause MG and these antibodies were found to be positive in 40-70% of seronegative patients in some studies. These MUSK+ patients tend to have more bulbar complaints such as speech problems, problems swallowing, drooling etc, rather that breathing problems and generalized fatigue. There are still a group of patients with MG that are seronegative and MUSK negative (with an unknown immune response against the neuro-muscular junction). In addition to the antibody tests, MG is also diagnosed with neuro-physiological tests such as EMG, RNS (Repetitive nerve stimulation) and SFEMG (single fiber EMG). Seronegative patients that are also MUSK- tend to have more abnormal RNS and SFEMG tests. The treatment for MG incldues long term immune suppression with agents such as cellcept, imuran, etc; prednisone (usually more short term due to side effects); and intermittent plasma exchange and/or IVIG. Mestinon is also used for some symptoms relief. Stopping predinsone and prograf to obtain a quality diagnostic study is a wise move. You want to be sure of a diagnosis before you undertake therapies that have risk associated with them (prednisone has many side effects, all immunosuppressants make you more vulnerable to infections). I would suggest that you have the SFEMG done, then continue your therapy. Some cases of MG are linked to a cancer of the Thymus gland (Thymoma) which is the reason to get the CT scan (Seronegative patients tend to have a lower incidence of thymoma). Seropostive and seronegative MG patients can have similar levels of clinical severity and the treatment for all remains the same.
I hope this has been helpful.
To my knoledge I have had all the tests available in the u.k for the diagnosis of occular m.g.I first started getting double vision when I was playing football about 15years ago,I had a scan and the 3rd disc in my spine was compressing my cord.I had the operation and everything seemed to be ok.My double vision returned a couple of months later.I regularly train and even run marathons with no problems except double vision.I have no muscle weakness at all and every test says I have not got occular m.g.I really dont know what else I can do.I have had another scan and my disc in my spine are ok