Colchicine toxicity — SCE Rheumatology MCQ

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HardRheumatological PharmacologyColchicine toxicitySCE Rheumatology

A 76-year-old man with CKD stage 4 takes colchicine for gout flare prophylaxis. He presents with diarrhoea, proximal weakness and paraesthesia. CK is 1,900 IU/L and neutrophils are 0.9 × 10⁹/L. He recently started clarithromycin for bronchitis. What is the most likely diagnosis?

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Correct answer: E — Colchicine toxicity

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

Colchicine toxicity is best because renal impairment plus macrolide interaction can precipitate colchicine toxicity with gastrointestinal symptoms, myopathy and marrow suppression. B is less suitable because SLE flare is less likely without lupus phenotype; C is less suitable because polymyositis does not explain clarithromycin interaction and neutropenia as well; D is less suitable because reactive arthritis is inflammatory oligoarthritis after infection; E is less suitable because fibromyalgia has normal CK and no neutropenia. Clinical pearl: colchicine has a narrow therapeutic index, especially with renal impairment and CYP3A4/P-gp inhibitors.

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/musculoskeletal-conditions