Immunopathology of skeletal muscle. The value of direct immunofluorescence in the diagnosis of connective tissue disease.

Whitaker and Engel in 1972 first described immunoglobulin deposition in muscle biopsy specimens in connective tissue disorders. In order to confirm and extend their observations and in the hope of identifying features that may differentiate skeletal muscle involvement in connective tissue diseases from other neuromuscular diseases, a series of 80 muscle biopsy specimens were examined using direct immunofluorescence. Three distinctive direct immunofluorescence patterns consisting of vascular, sarcolemma-basement membrane, and fiber staining were identified in skeletal muscle biopsy specimens from 35 patients, 31 of whom had a connective tissue disease. A vascular staining pattern showing a granular deposition of immunoglobulin or complement was seen in 15 patients, all of whom had a connective tissue disease. Routine stains generally did not reveal vessel abnormalities. A sarcolemma-basement membrane staining pattern was demonstrated around the sarcoplasmic membrane in 29 cases. Twenty-six of these patients had a connective tissue disease. There was no correlation with inflammation, fiber necrosis, or degree of connective tissue replacement. Fibers staining for immunoglobulin or complement, seen in 14 cases, generally occurred in morphologically normal fibers. Thirteen of these patients had a connective tissue disease. Since the pathologic change in muscle in the collagen vascular diseases often consists of the nonspecific findings of focal fiber necrosis frequently without inflammatory infiltrates, direct immunofluorescence may be useful in the diagnosis and classification of muscle diseases in the collagen vascular disorders. Furthermore, the findings of immunoglobulin deposition either within vessels or within individual muscle fibers suggest that immunological mechanisms may be responsible for muscular abnormalities in the connective tissue diseases.