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.
Swash M, Fox KP, Davidson AR. Carcinoid MyopathySerotonin-Induced Muscle Weakness in Man?. Arch Neurol. 1975;32(8):572–574. doi:10.1001/archneur.1975.00490500092014