A 62-year-old man with small cell lung carcinoma develops hyponatremia (Na+ 118 mEq/L), concentrated urine, and inappropriately elevated urine sodium. The paraneoplastic syndrome is mediated by ectopic secretion of:
- A Arginine vasopressin (ADH) ✓
- B PTH-related peptide
- C ACTH
- D Insulin-like growth factor 1
Correct answer: A. Arginine vasopressin (ADH)
Explanation
The clinical picture of hyponatremia with concentrated urine and elevated urine sodium despite low serum sodium is classic SIADH (syndrome of inappropriate ADH secretion). Small cell lung carcinoma is the most common cause of ectopic ADH production, as these neuroendocrine tumors retain secretory granules capable of producing neuropeptides. ACTH ectopic production causes Cushing syndrome; PTH-rP causes hypercalcemia; IGF-1 ectopic production causes hypoglycemia.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.