Myositis-Specific and -Associated Autoantibodies

Abstract

Twenty-five percent to 50% of patients with polymyositis (PM) and dermatomyositis (DM) have autoantibodies that are specific for or associated with the presence of myositis. Because of a relatively low sensitivity for the diagnosis of PM or DM, these autoantibodies are inadequate as a screening test for PM or DM in patients with suspected inflammatory myopathy. However, they may be used to support the diagnosis of myositis, and they help exclude the diagnosis of inclusion body myositis in which autoantibodies are infrequent. In addition, these antibodies are associated with homogeneous syndromes with the following reproducible clinical features and prognosis: (I) the antisynthetases generally occur with moderately severe myositis, often in association with interstitial lung disease. Raynaud's phenomenon, and arthropathy; (2) anti-SRP is a marker of severe PM with associated cardiac disease and high mortality; (3) anti-Mi-2 occurs in generally corticosteroid-responsive DM associated with a potentially severe rash; and (4) the myositis-associated autoantibodies anti-PM-ScI and anti-Ku portend a moderately favorable prognosis. Anti-PH-Scl occurs in systemic sclerosis, often in association with arthropathy and Raynaud's syndrome. Anti-Ku occurs in systemic sclerosis and other connective tissue diseases with or without myositis. Thus, both myositis-specific and -associated antibodies have clinical use in the diagnosis of PM and DM and are predictive of certain clinical syndromes and responses to treatment.