Ultrastructural and histochemical studies of muscle in rheumatoid arthritis.

Muscle biopsy material from 12 patients with rheumatoid arthritis was investigated by electron microscopy. Degenerative changes and atrophy of the muscle fibres were observed. The periphery of the fibre was indistinct and showed an increased content of lipofuscin granules and remnants of myofilaments. Mitochondria were frequent in the subsarcolemmal regions, but between the myofibrils these were rarer than in healthy subjects. The triads were often swollen and displaced. Capillaries were more frequent than in normal material; the endothelial cells and especially the basement membrane showed pathological changes. Satellite cells were frequent and are regarded as an indication of regeneration.