Skeletal muscle in polymyositis. Immunohistochemical study.

Thirty-two patients with adult-onset polymyositis uncomplicated by cancer or systemic connective tissue disease were studied. Muscle biopsy specimens were examined with direct immunofluorescence microscopy and results were compared with those in 94 control subjects. Sarcolemmal and sarcoplasmic staining were observed in both groups and considered to be nonspecific. Immune deposits in the muscle microvasculature were present in some cases of systemic lupus erythematosus and dermatomyositis but were not present in polymyositis. Our data suggest that the finding of vascular immunofluorescence excludes the diagnosis of adult polymyositis and implies that the pathogenesis of this disease and other idiopathic inflammatory myopathies may differ.