Polyarthritis due to Mycobacterium kansasii in a patient with rheumatoid arthritis.

A case of destructive polyarthritis due to infection by Mycobacterium kansasii is described in a 68-year-old patient with long-standing rheumatoid arthritis (RA) receiving prednisone and azathioprine therapy. Superimposed infection was suggested by positive Ziehl-Neelsen stains of synovial fluid from the patient's right shoulder and wrists, with confirmation on culture. Histological examination of synovium revealed abundant noncaseating granulomata within subsynovial cellular infiltrates. Treatment with triple antituberculous chemotherapy resulted in substantial extra-articular improvement within 3 months. However, articular destruction progressed unabated. A high index of suspicion is needed to diagnose joint infections in patients with underlying polyarthritis who are receiving immunosuppressive therapy. The progressive joint damage, despite periarticular resolution, may suggest the need for a combination of surgical synovectomy and antituberculous chemotherapy.