Mycobacterium avium-intracellulare septic arthritis of the sternoclavicular joint in an immunocompetent host; a three-year follow-up.

A 34 year-old lady was referred for rheumatology review by the orthopaedic team for further investigation of chronic left sternoclavicular joint pain. No preceding event such as trauma, injury or infection had occurred. A rheumatology workup turned out to be negative for an inflammatory arthropathy. After extensive investigations including blood tests, an MRI scan, a CT scan, and a bone scan, and in consultation with the orthopaedic team, the affected joint was biopsied and tested for mycobacterium avium-intracellulare infection. The results came back as positive and the patient was started on anti-mycobacterial treatment. We report the diagnosis, management and 3-year follow-up of this unique case. This highlights an uncommon and often misdiagnosed cause of septic arthritis caused by mycobacterium avium-intracellulare infection. To our knowledge this is the first confirmed sternoclavicular mycobacterium avium-intracellulare infection in an immunocompetent host reported in the literature.