A 58-year-old woman with a known small cell lung carcinoma develops hyponatremia with concentrated urine and normal renal, adrenal, and thyroid function. The paraneoplastic syndrome responsible is mediated by ectopic secretion of which peptide?

• A Adrenocorticotropic hormone (ACTH)
• B Parathyroid hormone-related protein (PTHrP)
• C Calcitonin
• D Antidiuretic hormone (ADH/AVP) ✓

Explanation

Small cell lung carcinoma is the classic cause of ectopic ADH secretion leading to SIADH, manifesting as dilutional hyponatremia with inappropriately concentrated urine despite normal renal, adrenal, and thyroid status. Ectopic ACTH causes Cushing syndrome, PTHrP causes humoral hypercalcemia of malignancy, and calcitonin is secreted by medullary thyroid carcinoma.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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