Abstract
A case of Mycobacterium avium arthritis in a 39-year-old female patient with mixed connective tissue disease (MCTD) was reported. An extra-articular abscess had formed outside the knee joint and extended down the calf. A culture was taken of the abscess and synovial fluid disclosed Mycobacterium avium. This was resistant to most anti-tuberculosis agents. A combination of anti-tuberculosis drugs followed a total resection of the abscess. We concluded that M avium septic arthritis could insidiously develop into an extra-articular abscess. A combination of anti-tuberculosis drugs with a total resection of the abscess was an effective treatment.