Rimmed vacuolar distal myopathy. An ultrastructural study.

An ultrastructural study of biopsied muscles was performed in seven patients with rimmed vacuolar distal myopathy, which was characterized by prominent rimmed vacuoles in the muscle fibers. The earliest changes noted were focal proliferation of the Golgi's apparatus and mitochondrial degeneration with myofibrillar loss. A proliferation of the T-system appeared later. Secondary lysosomes (autophagosomes) could be noted much later and gradually increased in number. Autophagosomes tended to coalesce and became larger autophagic vacuoles, which were surrounded in part by relatively preserved myofibrils and partly by a single membrane. Gently curved laminated structures (tubulomembranous structures) were seen in the degenerating muscle fibers and also in relatively intact fibers, satellite cells, and interstitial cells in all cases. They were closely associated with lipofuscin-like material. These findings suggest that an abnormality of the lysosomal system might be essential in the pathogenesis of rimmed vacuolar distal myopathy.