Mycobacterium kansasii causing chronic monoarticular synovitis in a patient with HIV/AIDS.

Mycobacterium kansasii is a nontuberculous mycobacterium that primarily causes pulmonary disease in AIDS patients, however it has also been known, rarely, to result in skeletal infection. When skeletal infection occurs, the time from onset of symptoms to diagnosis is up to 5 years in previously reported cases. We describe a 48-year-old woman with HIV/AIDS who presented with chronic, isolated left knee pain and swelling of over two decades which had recently worsened. Radiographs and magnetic resonance imaging demonstrated marked subarticular erosions, synovial thickening, and bone marrow edema, which had progressed compared with prior imaging done seven years earlier. Synovial biopsy grew Mycobacterium kansasii. Following the presentation of our case, clinical and imaging findings, including the differential diagnosis, of monoarticular arthritis caused by Mycobacterium kansasii are reviewed and discussed.