Immune-Mediated Colitis from Immunotherapy — SCE Palliative Medicine MCQ

Correct answer: C — Immune‑mediated colitis — an immune‑related adverse event of checkpoint inhibitors requiring prompt evaluation and high‑dose corticosteroid treatment

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

The most likely diagnosis is immune‑mediated colitis. Pembrolizumab, an immune checkpoint inhibitor, is well documented to cause immune‑mediated gastrointestinal toxicity, most critically colitis presenting with severe diarrhoea, abdominal pain, and bloody stools. UK protocols mandate urgent evaluation (e.g., stool studies, imaging, endoscopy) and high‑dose corticosteroid therapy for moderate to severe presentations. Viral gastroenteritis (B) generally is self‑limited and lacks the specific temporal relationship and severity. C. difficile (C) assumes recent antibiotic use, which is absent. Radiation colitis (D) requires prior irradiation, not described. A Crohn’s flare (E) requires pre‑existing disease. This stem tests recognition of a common, serious immunotherapy‑related toxicity and appropriate initial management.

Reference: South West London NHS Immune Checkpoint Inhibitor–induced Enterocolitis guideline (2026) and UKMI risk‑management materials for Keytruda (pembrolizumab) (2026)