Crystal shedding in septic arthritis: case reports and in vivo evidence in an animal model.

Two cases of coexisting septic and crystalline joint disease are reported. In one patient polyarticular septic arthritis occurred simultaneously with gout and pseudogout. In a second patient septic arthritis preceded the appearance of calcium pyrophosphate dihydrate (CPPD) crystals in the joint fluid, supporting an earlier postulate that lysosomal enzymes released during sepsis lead to shedding of crystals from cartilage and synovium into the joint space. This sequence was demonstrated in a rat air pouch model of synovium, in which CPPD crystals embedded in facsimile synovial tissue were released after injection of pyogenic bacteria. Coexisting septic arthritis should always be considered when crystals are identified in inflamed joints, particularly in elderly patients with concurrent infections.