Reactive arthritis — SCE Rheumatology MCQ

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EasySpondyloarthropathiesReactive arthritisSCE Rheumatology

A 25-year-old man develops an acutely swollen right knee and bilateral heel pain 3 weeks after an episode of urethritis, which resolved before the joint symptoms began. He is afebrile. Examination shows Achilles enthesitis, conjunctival injection and circinate balanitis. Synovial fluid is inflammatory, but Gram stain and culture are negative. His CRP is 74 mg/L. What is the most likely diagnosis?

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Correct answer: B — Reactive arthritis

The diagnosis is reactive arthritis. The discriminating features are acute lower-limb arthritis and Achilles enthesitis beginning 3 weeks after urethritis, together with conjunctivitis and circinate balanitis. This is the characteristic post-infectious spondyloarthritis pattern. Septic arthritis must always be excluded in an acutely swollen joint, but the afebrile, multisystem post-infectious presentation and negative Gram stain and culture favour reactive arthritis. Gonococcal arthritis may follow genital infection but does not characteristically produce this combination of enthesitis, conjunctivitis and circinate balanitis. Behçet disease is associated with recurrent oral and genital ulceration rather than circinate balanitis, while rheumatoid arthritis would usually cause persistent symmetrical polyarthritis.

Reference: NHS. Reactive arthritis, symptoms and diagnosis. Last reviewed 16 December 2024. https://www.nhs.uk/conditions/reactive-arthritis/