[Muscle biopsy in the diagnosis of polymyositis. Apropos of 13 cases].

Muscle biopsies from 13 patients with polymyositis were studied with light microscopy, histoenzymology and electron microscopy. Light microscopy often shows degenerative muscle fibers and endomysial collections of inflammatory cells. These findings are helpful for the diagnosis but are not consistent. Histoenzymology may other features such as perifascicular atrophy, and alterations in cytoplasmic staining patterns, but these changes are non specific. Electron microscopy frequently reveals vascular changes, especially pseudoviral inclusions, which are the most reliable factors and the most frequently observed changes in ultrastructural diagnosis.