Sulfasalazine adverse effect — SCE Rheumatology MCQ

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ModerateRheumatological PharmacologySulfasalazine adverse effectSCE Rheumatology

A 40-year-old man with psoriatic arthritis starts sulfasalazine. Four weeks later he develops sore throat, mouth ulcers and fever. FBC shows neutrophils 0.3 × 10⁹/L. LFTs are normal and there is no rash. What is the most likely diagnosis?

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Correct answer: B — Sulfasalazine-induced agranulocytosis

Explanation lettering: E = shown as A · C = shown as B · A = shown as C · B = shown as E

Sulfasalazine-induced agranulocytosis is best because early severe neutropenia with fever after sulfasalazine initiation indicates drug-induced agranulocytosis. A is less suitable because gout flare does not cause agranulocytosis; B is less suitable because hydroxychloroquine retinopathy causes visual changes after longer exposure; D is less suitable because reactive arthritis flare does not cause profound neutropenia; E is less suitable because methotrexate pneumonitis causes respiratory symptoms and diffuse lung change. Clinical pearl: early blood monitoring is particularly important after starting csDMARDs.

Reference: BSR csDMARD guideline 2025; BNF