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Myasthenia Gravis

Effects of mestinon

03/21/2008

Question:

If the diagnosis of mg is questionable would giving the patient mestinon help with the diagnosis. What effects would it have on the patient if they didn`t have mg. Seems like giving the medication would help to diagnose mg.

Answer:

I have used mestinon (pyridostigmine) to help with patients with symptomatic myasthenia, and rarely to help with the diagnosis. I do not base my diagnosis on their response to pyridostigmine alone. It would be like diagnosing knee arthritis by relief of the pain with Tylenol; the pain may be better, but it doesn't tell me what the underlying pathology is. It is symptomatic therapy and may only support the diagnosis. Not everyone responds to mestinon. Not everyone who responds to mestinon has myasthenia.

The Tensilon (edrophonium) test has been studied more. It has a sensitivity that has been quoted at 60% and a lower specificity (meaning other diseases can have the same response as a myasthenic would). The test is also very subjective and I would not base immunosuppressant therapy on a Tensilon test alone.

Mestinon does have side effects and it should be used with caution. The drug can cause increased weakness, can provoke fasciculations (painless quivering muscle), can cause muscle cramping, stomach cramps and diarrhea, nausea, flushing, tearing, and runny nose. It can also cause slowed heart rates and bronchospasm (airways close down). When used on people without myasthenia, I have seen the diarrhea/stomach cramps and muscle cramps/fasciculations most commonly.

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Response by:

Robert W Neel, IV, MD Robert W Neel, IV, MD
Assistant Professor of Neurology
College of Medicine
University of Cincinnati