Snapshot A 22-year-old man presents to his primary care physician's office due to pain in his knee, dysuria, and eye discomfort and discharge. Medical history is significant for a sexually transmitted infection due to Chlamydia approximately 1 month ago. On physical exam, there is conjunctivitis, left-knee swelling and tenderness, and urethral discharge. Introduction Clinical definition a systemic inflammatory disorder that results from following an extra-articular infection (e.g., sexually transmitted infection and gastroenteritis) typically results after 1-6 weeks after the infection formerly known as Reiter syndrome classic triad is urethritis conjunctivitis arthritis Epidemiology demographics age 20-40 years of age sex following a genitourinary infection, it is more common to develop reactive arthritis in men affects men and women equally a gastrointestinal infection risk factors HLA-B27 positivity Etiology genitourinary pathogens Chlamydia trachomatis gastrointestinal pathogens Salmonella enteritidis and typhimurium Shigella Yersinia Campylobacter Pathogenesis unclear Prognosis most cases spontaneously recover Presentation Symptoms asymmetric joint pain e.g., knee, ankle, and heel eye discomfort in cases of conjunctivitis Physical exam conjunctivitis arthritis typically an acute and asymmetric oligoarthritis genital involvement circinate balanitis urethritis cervicitis keratoderma blennorrhagicum Studies Labs complete blood count may demonstrate neutrophillic leukocytosis ↑ C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) Diagnostic criteria a clinical diagnosis Differential Ankylosing spondylitis Enteropathic arthritis Septic arthritis Gonococcal arthritis Gout Pseudogout Rheumatoid arthritis Treatment Medical nonsteroidal antiinflammatory drugs (NSAIDs) indication drug of choice for acute phase of reactive arthritis