Antibodies to nuclear antigens in polymyositis: relationship to autoimmune 'overlap syndromes' and carcinoma.

Thirty-two patients with polymyositis were categorised into 4 groups: (1) 'pure' polymyositis, (2) dermatomyositis, (3) myositis associated with autoimmune 'overlap syndrome', and (4) those with associated malignancy. Serum from each patient was examined for a range of antinuclear antibodies. Seventeen patients had ANA detected by immunofluorescence, 18 patients had raised DNA binding (greater than 25 U/ml), of whom eight had levels greater than 50 U/ml (SI conversion: U/l = U/ml x 10(3)). Antibodies to soluble nuclear antigens were detected in 23 (72%) by 1 or more of 3 methods, and in all of these anti-RNP was the main antibody detected. Antibodies to other soluble antigens were also present in 6 sera. In 2 cases, both patients with SLE/myositis overlap, these were shown to be anti-Sm. The remaining 4 had antibodies to various protein components of the extracts, but it was not possible to demonstrate an antibody of diagnostic specificity for polymyositis. Furthermore, quantitation of anti-RNP and anti-DNA antibodies failed to define a distinct clinical entity or exclude malignant disease. High levels of anti-RNP antibodies showed an association with Raynaud's phenomenon, sclerodactyly, and pulmonary fibrosis and an inverse correlation with the rash of dermatomyositis, suggesting that this antibody may be of pathogenetic rather than diagnostic significance.