Patients with arthritis and anti-U1-RNP antibodies: a 10-year follow-up.

Five hundred and forty patients attending a rheumatology ward were screened for antinuclear antibodies (ANA) by indirect immunofluorescence (IFL). Seventy had a significant titre of ANA. Twenty-three had U1-ribonucleoprotein antibodies (U1-RNP-ab). The clinical findings in U1-RNP-ab-positive patients were consistent with mixed connective tissue disease (MCTD). Disease was more serious in the U1-RNP-ab-positive patients in terms of polyarthritis severity as well as mortality due to rheumatic disease. Thus, in this arthritis patient population, U1-RNP-ab positivity predicted an aggressive disease characterized by an erosive arthritis.