Question

Secretory diarrhoea does NOT occur in

• A. Medullary thyroid carcinoma
• B. Malignant carcinoid syndrome
• C. Villous adenoma of the rectum
• D. Congenital chloridorrhea

Hint:

Separate causes driven by a circulating hormone or transporter defect from a cause that is a local mucosal tumour effect.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question lists four conditions and asks which one is NOT a recognised cause of secretory diarrhoea, where diarrhoea persists even on fasting because the gut is actively secreting fluid and electrolytes rather than simply failing to absorb an unabsorbed solute.

Step 2: Key Concept or Approach:
Classic secretory diarrhoea is driven by a circulating hormone or peptide that raises intracellular cAMP or cGMP in enterocytes, switching them from net absorption to net chloride and fluid secretion, or by a primary transporter defect that does the same thing congenitally. The question is testing which of the four listed conditions fits that hormonal or transporter mechanism and which one causes diarrhoea through a different route.

Step 3: Working Through the Options:
Medullary thyroid carcinoma secretes calcitonin and related peptides that drive cAMP-mediated intestinal secretion, producing a classic secretory diarrhoea. Malignant carcinoid syndrome releases serotonin and other vasoactive peptides into the systemic circulation once hepatic metastases bypass first-pass clearance, and this drives a hormonally mediated secretory diarrhoea as part of the syndrome. Congenital chloridorrhea is a primary defect of the intestinal chloride-bicarbonate exchanger, causing lifelong secretory diarrhoea with high faecal chloride from birth - a textbook example of a transporter-based secretory process. Villous adenoma of the rectum, in the answer intended here, is treated as the exception: its diarrhoea is attributed mainly to the tumour's bulky mucus output and local mechanical effects at the mucosal surface rather than to a systemic hormone acting on the whole bowel, distinguishing it from the other three, more classically hormone-driven processes in this list.

Step 4: Conclusion:
Secretory diarrhoea, in the sense being tested here, is NOT the mechanism attributed to villous adenoma of the rectum among these four options.