Reactive arthritis, also called Reiter's syndrome, is the most common type of inflammatory polyarthritis in young men. It is sometimes the first manifestation of human immunodeficiency virus infection. An HLA-B27 genotype is a predisposing factor in over two thirds of patients with reactive arthritis. The syndrome most frequently follows genitourinary infection with Chlamydia trachomatis, but other organisms have also been implicated. Treatment with doxycycline or its analogs sometimes shortens the course or aborts the onset of the arthritis. Reactive arthritis may also follow enteric infections with some strains of Salmonella or Shigella, but use of antibiotics in these patients has not been shown to be effective. Reactive arthritis should always be considered in young men who present with polyarthritis. Symptoms may persist for long periods and may, in some cases, cause long-term disability. Initial treatment consists of high doses of potent nonsteroidal anti-inflammatory drugs. Patients with large-joint involvement may also benefit from intra-articular corticosteroid injection. (Am Fam Physician 1999;60:499-507.)

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LABORATORY FINDINGS Synovial Fluid WBC 100/ul-43m000/ul (avg 18,500); 60% neutrophils Poor mucin clot Increased protein Glucose usually normal but may be low when the leukocyte count is high *Positive blood culture, when there is systemic dissemination, may be the only source of microbial identification. Normal or increased complement Presence of "Reiter's cells" (macrophages with partially digested neutrophils) Blood Leukocytosis (10,000/ul-20,000/ul) Increased sedimentation rate - parallels the clinical course Increased serum complement - reflects active inflammation Increased serum globulins - in chronic disease Presence of HLA-B27 antigen in 75% of patients Negative rheumatoid factor Other Laboratory Findings Increased WBC in urine and prostatic fluid - reflects urethritis. Negative cultures of blood, synovial fluid, and urethral discharge