A 58-year-old man reports profuse gelatinous mucus discharge per rectum for months, with lethargy and cramps. Serum potassium is 2.6 mmol/L. Proctoscopy shows a large, soft, velvety sessile lesion carpeting the lower rectum. Biopsy confirms a villous adenoma. What is the mechanism of his hypokalaemia?
- A Renal potassium wasting caused by prostaglandin secretion
- B Secondary hyperaldosteronism from chronic volume depletion
- C Secretion of potassium-rich mucus by the tumour epithelium ✓
- D Malabsorption of potassium due to mucosal replacement by tumour
Correct answer: C. Secretion of potassium-rich mucus by the tumour epithelium
Explanation
Villous adenomas secrete large volumes of mucus rich in potassium and protein, and the resulting faecal loss of potassium produces the classic triad of mucus diarrhoea, hypokalaemia, and dehydration. Aldosterone rises secondarily as a response to volume depletion but is not the primary mechanism. Large villous lesions also carry a substantial risk of occult malignancy and require complete excision.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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