Antibody to extractable nuclear antigen in the rheumatic diseases.

Two hundred and eighty-four patients with various rheumatic diseases were studied for the prevalence of antibodies to extractable nuclear antigen (anti-ENA) using an improved haemagglutination technique. Anti-ENA rarely occurred in patients with rheumatoid arthritis, scleroderma, polymyositis, dermatomyositis and Sjögren's syndrome. Seventeen per cent (13/72) of patients fulfilling at least four preliminary ARA criteria for systemic lupus erythematosus (SLE) demonstrated anti-ENA. The predominant antibody was directed at ribo-nuclease-resistant ENA (anti-Sm). Antibodies to ribo-nuclease-sensitive ENA (anti-RNP) occurred in the minority of patients with SLE (2/72) and the mixed connective tissue disease syndrome (MCTD). A trend toward an increased incidence of renal disease in SLE patients with anti-Sm was present. Sequential analysis of anti-Sm in patients with SLE showed a fall in titre paralleling the normalization of anti-DNA antibody titres and serum complement values. No case of unrecognized MCTD was uncovered in our rheumatic disease population.