An aseptic (that is, not involving infection) ARTHRITIS provoked by an immune reaction to an episode of infection elsewhere in the body. It often occurs in association with ENTERITIS caused by Salmonella (see FOOD POISONING) and certain SHIGELLA strains, and in both YERSINIA and CAMPYLOBACTER enteritis. Non-gonococcal urethritis, usually due to CHLAMYDIA, is another cause of reactive arthritis; REITER'S SYNDROME is a particularly florid form, characterised by MUCOUS MEMBRANE, skin and eye lesions.

The SYNOVITIS usually starts acutely and is frequently asymmetrical, with the knees and ankles worst affected. Often there are inflammatory lesions of tendon sheaths and entheses (bone and muscle functions) such as PLANTAR FASCIITIS. The severity and duration of the acute episode are extremely variable.