The laboratory diagnosis of mild myasthenia gravis

We report our experience with single‐fiber electromyogrphy (SF‐EMG), acetylcholine receptor antibody assays, and Lancaster Red‐Green tests of ocular motility with edrophonium chloride in the diagnosis of myasthenia gravis (MG). Over a period of almost 3 years, 43 patients in whom repetitive‐stimulation nerve conduction tests were nondiagnostic had SF‐EMG studies; 34 (79%) were positive. Examination of more proximal muscles yielded a higher likelihood of positive results. Anti‐acetylcholine receptor antibodies were detected in 25 (71%) of 35 patients whose sera were assayed, and Lancaster Red‐Green tests of ocular motility were positive in 13 (81%) of 16 patients studied. No single test was superior in diagnosing MG, but the three were complementary. If patients with mild MG are tested by all three methods, at least 95% should have laboratory confirmation of MG.