Radioimmunoassay for antibodies to human skeletal muscle myosin in serum from patients with polymyositis.

Antibodies to human skeletal muscle myosin were detected in 90% of sera from patients with polymyositis by radioimmunoassay using purified human myosin as antigen, and the mean titre was 4.24 X 10(-10)M. The incidence and the mean titre of anti-myosin antibodies were significantly higher than in patients without polymyositis. Anti-myosin antibody titres correlated with steroid therapy in polymyositis patients. Titres in untreated patients with polymyositis correlated with the severity of muscle weakness. Radioimmunoassay for anti-myosin antibodies should prove to be useful in the diagnosis of polymyositis and the evaluation of clinical state.