Which one of the following is the most sensitive test for the diagnosis of myasthenia gravis?
Correct Answer: Positive edrophonium test
Description: Diagnosis of myasthenia gravis (MG) History:--diplopia, ptosis, weakness, fluctuation, and fatigue, worse with activity, improved by rest Physical examination:--ptosis, diplopia, motor power survey--quantitative testing of muscle strength, forward arm abduction time (5 min), vital capacity, the absence of other neurologic signs. Laboratory testing:--anti-AChR radioimmunoassay--85% positive in generalized MG, 50% in ocular MG, the definite diagnosis of positive; negative results do not exclude MG, 40% of AChR antibody-negative patients with generalized MG have anti-muscle antibodies. Repetitive nerve stimulation, the decrement of>15% at 3Hz: highly probable. Single fiber electromyography: blocking and fitter, with normal fiber density; confirmatory, but not specific. Endorphin chloride--(Tensile) 2 mg + 8 mg IV: highly probable diagnosis if unequivocal positive. For ocular or cranial MG, exclude intracranial lesions by CT or MRI. Ref - Harrison's internal medicine 20e pg 3233-3235, 3234t, 3237t
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