Myasthenia gravis associated with small-cell carcinoma of the lung.

A 49-year-old man complained of a 3-month history of progressive generalized muscle weakness. He was diagnosed as having small-cell lung carcinoma at the same time. He received an intravenous injection of edrophonium chloride with remarkable improvement of muscle strength. Electromyographic studies revealed a compound muscle action potential that decreased after repetitive stimulation. These findings were considered representative of myasthenia gravis (MG), and inconsistent with Eaton-Lambert syndrome. The appearance of MG with small-cell lung carcinoma seems to be very rare, but possible.