BACKGROUND: Rheumatoid arthritis tenosynovitis is difficult to discriminate from non-tuberculous tenosynovitis on the basis of radiological and pathological findings.

CASE REPORT: A 74-year-old woman with a 4-year history of rheumatoid arthritis was referred to our hospital to undergo treatment for uncontrollable tenderness and swelling in her right third metacarpophalangeal joint, right wrist, and left knee joint. In the previous year, she underwent surgery at a local hospital for the swelling in her right metacarpophalangeal joint, the information of which was not known precisely, but the swelling subsided in due course after an operation. We treated the patient with infliximab (monthly intravenous infusions of 150 mg), but 2 months later, she complained of exacerbation of the swelling in her right third metacarpophalangeal joint and right wrist, and fluid discharge that contained Mycobacterium intracellulare. After synovectomy and aggressive debridement in the palmar side of the right wrist, she was diagnosed as having granulomatous tenosynovitis caused by the M. intracellulare infection and abundant rice body formation in the right carpal tunnel area. We considered the rice bodies inside and outside the bursa, along with a history of tenosynovitis exacerbation after initiation of infliximab therapy (tumor necrosis factor alpha inhibitor [TNFi]), to be related to the M. intracellular infection.

CONCLUSIONS: Tenosynovitis caused by atypical mycobacteria is uncommon and usually affects the hand or wrist. Therefore, for early diagnosis, mycobacterial infection should be considered in cases of indolent chronic granulomatous tenosynovitis, especially in RA cases that recur after TNFi therapy is started.

Keywords: Arthritis, Rheumatoid, Granulomatous Disease, Chronic, Nontuberculous mycobacteria