Mycobacterium avium/Mycobacterium intracellulare complex-associated arthritis masquerading as a seronegative rheumatoid arthritis

Mycobacterium avium/Mycobacterium intracellulare complex (MAC) is a rare ca use of tenosynovitis. We describe a case in which a previously healthy pati ent developed bilaterally symmetric synovitis and was treated with disease modifying anti rheumatic drugs (DMARDs); the synovitis progressed into a bi laterally symmetric chronic granulomatous tenosynovitis that was uncontroll able despite a synovectomy and DMARD therapy. Three years after developing symptoms, and 21/2 years after her diagnosis of rheumatoid arthritis, MAC w as cultured from synovial fluid. All DMARDS were stopped, and the patient r eceived a total of 24 months of triple antibiotic therapy. All swelling and stiffness resolved after 7 months of therapy. The patient remains asymptom atic two months after completion of antibiotic therapy. Rheumatologists and other arthritis specialists need to include MAC in their differential diag nosis of seronegative symmetrical inflammatory arthritis.