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Carcinoid syndrome — MCCQE Part 1 MCQ

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HardDiarrheaCarcinoid syndromeMCCQE Part 1

A 59-year-old has episodic facial flushing, chronic watery diarrhoea, and intermittent wheeze. CT shows an ileal mass with multiple liver lesions. Twenty-four-hour urinary 5-hydroxyindoleacetic acid is markedly elevated. Which diagnosis best unifies these findings?

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Correct answer: B — Metastatic ileal neuroendocrine tumour causing carcinoid syndrome

Flushing, secretory watery diarrhoea, and bronchospasm together with a markedly elevated 5-HIAA level identify carcinoid syndrome. An ileal neuroendocrine tumour often becomes clinically secretory after liver metastases allow vasoactive products to bypass hepatic first-pass metabolism. The diagnosis should prompt multidisciplinary neuroendocrine-tumour assessment, symptom control with a somatostatin analogue when appropriate, tumour staging, and echocardiographic assessment when carcinoid heart disease is suspected. Phaeochromocytoma more often produces episodic headache, palpitations, diaphoresis, and hypertension. Mast-cell disease can cause flushing and wheeze but does not fit the ileal mass, liver metastases, and elevated 5-HIAA pattern. VIPoma causes profound secretory diarrhoea with hypokalaemia and achlorhydria rather than this classic triad. Medullary thyroid carcinoma is associated with a thyroid primary and calcitonin, not an ileal primary with serotonin-metabolite elevation.

Reference: Cancer Care Ontario neuroendocrine tumour guideline: https://www.cancercareontario.ca/sites/ccocancercare/files/guidelines/full/pebc2-21v2f.pdf ; ENETS carcinoid-syndrome guidance: https://pmc.ncbi.nlm.nih.gov/articles/PMC9539661/