Amoebic Colitis vs Crohn's — RACP Adult Medicine MCQ

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HardInfectious DiseasesAmoebic Colitis vs Crohn'sRACP Adult Medicine

A 40-year-old man presents with a 3-week history of intermittent bloody diarrhoea. He recently completed a course of ciprofloxacin for traveller's diarrhoea. Colonoscopy shows segmental colitis with aphthous ulcers predominantly in the right colon. Biopsies show acute and chronic inflammation with granulomas. What is the most likely diagnosis?

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Correct answer: E — Amoebic colitis

Segmental colitis with aphthous ulcers, predominantly right-sided, with granulomatous inflammation in a traveller raises concerns for both Crohn's disease AND amoebic colitis. However, post-travel bloody diarrhoea with right-sided predominance and granulomas should prompt investigation for amoebic colitis (Entamoeba histolytica) before diagnosing IBD. Amoebic colitis can mimic Crohn's disease histologically (granulomas are formed around amoebic trophozoites). Serology and stool antigen/PCR for E. histolytica must be checked. Starting immunosuppression for presumed Crohn's in a patient with undiagnosed amoebic colitis can cause fulminant, fatal amoebic disease.

Reference: eTG – 2025 – Antibiotic Guidelines; eTG – 2025 – Gastrointestinal