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Research Center

Distinguishing Between Probable and Definitive Myasthenia Gravis



I went three years without my MG diagnosis (ocular and generalized). I finally got diagnosed in February via a Tensilon test and clinical exam by a national MG expert. Mestinon has helped, but I am getting worse lately, especially with the onset of asthma. I went to the Mayo Clinic to discuss new treatments and they are refusing to call me anything but "probable" MG because I haven`t tested positive to an EMG (I am seronegative too). Either I have MG or I don`t (and it is obvious I do have it). What is the point of using these kind of semantics when it is obvious a patient has MG? I reacted strongly and immediately to the first small dose of Tensilon (evidenced by ptosis and upper body strength improvement). Is there some kind of national guideline that says a Tensilon test isn`t enough for an MG diagnosis? Thank you for any input you can give me. I`m quite frustrated!


There are not national guidelines established by any body, but many experts have categorized patients by certain criteria using the terms "definite" and "probable". These are important for research studies of myasthenia gravis. One needs to be absolutely sure before entering a patient into a research study that the patient has MG and therefore objective tests like antibody tests and EMG are critical in defining patients. In my opinion the more important issue for patients is the diagnosis of the treating neurologist and how it impacts on your care. If your neurologist feels they have made a diagnosis of MG based on your examination and response to Tensilon, then I presume they would proceed to optimizing treatment based on their diagnosis. Physicians and patients do at times need to deal with diagnostic uncertainty.

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Response by:

Henry J Kaminski, MD Henry J Kaminski, MD
Formerly, Professor of Neurology
School of Medicine
Case Western Reserve University