The arthritis of mixed connective tissue disease.

Twenty patients with mixed connective tissue disease were followed for 5 years. Arthritis occurred in all 20 patients, being the presenting complaint in 11 patients. The joints most frequently involved were the proximal interphalangeal (PIP), metacarpophalangeal (MCP), wrists, metatarsophalangeal (MTP), and knee; the distribution tended to be symmetrical, mimicking early rheumatoid arthritis. Joint deformities occurred in 6 patients, but apart from 1 patient with arthritis mutilans, significant functional impairment was not encountered. Radiologically small punched out bone erosions, asymmetrically distributed, were the most characteristic finding; other notable changes were aseptic necrosis, tuft erosions, and periarticular calcification. Joint effusions were non-inflammatory, the cellular content was predominantly lymphocytic and the C3 level was normal. Most cases were controlled with non-steroidal anti-inflammatory agents and invariably responded to prednisone less than or equal to 7.5 mg/day.