The most sensitive test for the diagnosis of myasthenia gravis is:
A. Elevated serum ACh-receptor binding antibodies
B. Repetitive nerve stimulation test
C. Positive edrophonium test
D. Measurement of jitter by single fibre electromyography
Correct answer : C. Positive edrophonium test
Edrophonium test has 95% sensitivity for detection of systemic myasthenia gravis and 85% sensitivity for that of ocular variety.
(Note : This is the answer given in Mudit Khanna. But Harrison writes that it is used infrequently to diagnose MG and is limited to situations when other investigations do not yield a conclusive diagnosis. Other sources state single fibre electromyography to be the most sensitive test.)