Distal myopathy: histochemical and ultrastructural studies.

In three familial cases and one sporadic case of late-onset distal myopathy, muscle wasting started in the distal portions of the lower extremities. The most striking change seen by light microscopy was the appearance of rimmed vacuoles. These were presumed to be autophagic, because they were found by electron microscopy to contain membranous lamellar structures and other heterogenous materials enclosed by a limiting membrane. On the other hand, lysosomal activity was markedly increased in skeletal muscle. In 6% to 22% of affected muscle fibers there were acid phosphatase-positive granules deep in the sarcoplasm, whereas control muscles had no such granules. The degenerative process in distal myopathy may be different from that in other muscular dystrophies.