Carcinoid myopathy. Serotonin-induced muscle weakness in man?

A myopathy, which improved with cyproheptadine hydrochloride therapy, developed in a patient with carcinoid syndrome of ten years' duration. Biopsy examination revealed advanced atrophy of type II muscle fibers, with type I fiber preponderance. Many of the small fibers had degenerated. Carcinoid myopathy may be due to excess circulating serotonin.