Circulating autoantibody to muscle protein in a patient with paraneoplastic myositis and colon cancer.

A muscle-specific autoantibody was found in a patient with paraneoplastic myositis and colon cancer. By immunoblotting, we found high titers of circulating antibody to a 34-kDa neutral protein in the soluble sarcoplasmic fraction of the rat skeletal muscle. The serum did not react at all with other tissue extracts including the central nervous tissue, liver, or kidney. The possible role of this muscle-specific autoantibody in the pathogenesis of paraneoplastic myositis is discussed.