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Reactive Arthritis — SCE Infectious Diseases MCQ

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ModerateSTIsReactive ArthritisSCE Infectious Diseases

A 25-year-old man presents with a 3-day history of acute monoarthritis of the right knee. He has urethritis and bilateral conjunctivitis. He recently had unprotected sexual intercourse. Synovial fluid aspiration shows 35,000 WCC/µL (80% neutrophils), no crystals, and negative Gram stain. NAAT of first-void urine is positive for Chlamydia trachomatis. What is the most likely diagnosis?

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Correct answer: A — Reactive arthritis (sexually acquired)

The classic triad of urethritis, conjunctivitis, and arthritis following a genitourinary infection (Chlamydia trachomatis in this case) is consistent with sexually acquired reactive arthritis (formerly Reiter syndrome). The joint is inflamed but culture-negative (unlike gonococcal arthritis where N. gonorrhoeae may be cultured). The underlying STI should be treated (Doxycycline 100 mg BD for 7 days for chlamydia). NSAIDs are the mainstay of joint management.

Reference: BASHH 2019 – Chlamydia guidelines; BSR 2023 – Reactive arthritis