Mycobacterium avium/Mycobacterium intracellulare Complex-Associated Arthritis Masquerading as a Seronegative Rheumatoid Arthritis.

Mycobacterium avium/Mycobacterium intracellulare[cf1] complex (MAC) is a rare cause of tenosynovitis. We describe a case in which a previously healthy patient developed bilaterally symmetric synovitis and was treated with disease modifying anti rheumatic drugs (DMARDs); the synovitis progressed into a bilaterally symmetric chronic granulomatous tenosynovitis that was uncontrollable despite a synovectomy and DMARD therapy. Three years after developing symptoms, and 2 1/2 years after her diagnosis of rheumatoid arthritis, MAC was cultured from synovial fluid. All DMARDS were stopped, and the patient received a total of 24 months of triple antibiotic therapy. All swelling and stiffness resolved after 7 months of therapy. The patient remains asymptomatic two months after completion of antibiotic therapy. Rheumatologists and other arthritis specialists need to include MAC in their differential diagnosis of seronegative symmetrical inflammatory arthritis.