A condition probably caused by an immunological response to a virus (see IMMUNITY), in which the patient has URETHRITIS, ARTHRITIS and conjunctivitis (see under EYE, DISORDERS OF). The skin may also be affected by thickened areas. This is the most common cause of arthritis in young men and usually develops in people who have a genetic predisposition: thus, around 80 per cent of sufferers have the HLA B27 tissue type (see HLA SYSTEM). Treatment is symptomatic with ANALGESIA and NON-STEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS). (See also REACTIVE ARTHRITIS.)