A 62-year-old man with a known small bowel neuroendocrine tumor presents with episodic facial flushing, watery diarrhea, and wheezing. Echocardiography reveals tricuspid valve fibrosis. Urinary 5-HIAA is elevated. Which substance is primarily responsible for the flushing episodes in this patient?
- A Serotonin
- B Bradykinin ✓
- C Histamine
- D Prostaglandin E2
Correct answer: B. Bradykinin
Explanation
Carcinoid syndrome occurs when vasoactive substances from a neuroendocrine tumor reach systemic circulation via hepatic metastases or retroperitoneal spread. Flushing is primarily mediated by bradykinin and tachykinins, not serotonin. Serotonin causes diarrhea and valve fibrosis. Histamine-mediated flushing is seen in systemic mastocytosis, not typical midgut carcinoid.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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