A chronic myopathy with coated vesicles and tubular masses.

Two muscle biopsies from a 38-yr-old man with a lifelong mild chronic nonprogressive myopathy, showed accumulations of randomly oriented tubules of T-tubular origin, some of which had become greatly dilated and had accumulated osmiophilic material. The tubular masses lacked oxidative enzyme activity but during their evolution acquired esterase and acid phosphatase activity. Tubular areas appeared to break down and lead to intrusions of extracellular space into the center of fibers. Coated vesicles were numerous and often appeared to arise from the tubules. No abnormality could be detected on SDS PAGE electrophoresis of fractions from sucrose gradients.