Carcinoid myopathy and treatment with cyproheptadine (Periactin)

Abstract

A case of the carcinoid syndrome associated with a proximal myopathy is reported. Histology showed advanced atrophy of type II muscle fibers but no inflammation. Perinuclear acid phosphatase was increased. Electron microscopy revealed persistence of the Z line until the muscle fiber had been severely disrupted. Similar lesions have been observed in the hereditary muscular dystrophy in mice, and also in these animals and in rats when injected with 5 hydroxytryptamine (5 HT). Treatment with cyproheptadine caused a documented response in the patient's debilitating diarrhea and also produced symptomatic improvement in her muscular power. It is suggested that the myopathy is due to circulating 5 HT or is a nonmetastatic complication of the carcinoid tumor.