Double Vision

My son is 19 and recently dx with MG, his only complaints are double vision. He has had CT, MRI, Labs which all came back Negative. He was started on Mestinon 60mg TID, which did not improve his vision, so they said to increase his dose to 120mg
QID, after his 2nd dose of 120mg, he had abdominal pain and Increased muscle weakness, he was told to stop the medication.
that was on tuesday... On Thursday he had an EMG which showed
muscle weakness. My concern is the medication at such a high dose made him weak, everything I have read was to stop the midication 3-6 days before having the EMG since it can cause a false Positive.  
Could the medication of caused his test to be positive?
He is now On 80 mg of Prednisone daily for the last 11 days
and he still is haveing double vision.
How long will it take for the Predinose to correct the double vision?

thank you
Debrn12

[CCF-Neuro-M.D.-PW]

I don't know which tests were used to diagnose your son with MG, so I cannot comment on the accuracy of the diagnosis.

Ocular MG, or MG just associated with eye muscles, occurs in up to 30% of MG cases, although some later develop generalized MG.

Too much mestinon (which increases cholinergic stimulation) can result in side effects sich as diarrhea, increased tearing, muscle weakness, and severe muscle weakness known as 'cholinergic crises', sometime hard to seperate from an attack of generalized MG.

Mestinon can cause abnormalities on teh EMG, so testing is ideally not on mestinon - if the diagnosis is in doubt this may need to be repeated.

Prednisone does take up to 2-3 weeks to start working, and MG can become worse when it is started initially. Depending on the accuracy of the diagnosis, predisone may or may not correct the symptoms.

Good luck