Polyarticular Clostridium perfringens pyoarthritis.

A woman with rheumatoid arthritis presented with an abdominal mass and Clostridium perfringens septic arthritis in both wrists and shoulders. We believed this to be the first reported case of polyarticular septic arthritis due to Clostridium perfringens. Apatite, lipid, and cholesterol crystals in the shoulder joint effusions were a potential source of diagnostic confusion.