Vascular Deposits of Immunoglobulin and Complement in Idiopathic Inflammatory Myopathy

By a direct immunofluorescent technic granular deposits of IgG, IgM and C3, alone or in combination, were found in skeletal-muscle blood-vessel walls of 17 of 39 patients with idiopathic inflammatory myopathy. There was an especially high rate (nine of 11) in childhood dermatomyositis. In 142 other patients comprising the control group, only nine, most with disorders known to involve the immune system, had intramuscular vascular deposits of IgG or IgM. Deposition of immunoglobulin and C3 in structurally abnormal muscle fibers was found in a wide variety of diseases. A vascular abnormality mediated through deposits of immunoglobulin and C3, possibly in the form of immune complexes, is hypothesized as one of the mechanisms of muscle injury in certain cases of idiopathic inflammatory myopathy, particularly in dermatomyositis of children.