Three days after transsphenoidal surgery, a patient passes 6 litres of dilute urine daily with serum sodium 148 mEq/L and urine osmolality 110 mOsm/kg. After desmopressin administration, urine osmolality rises to 480 mOsm/kg. What is the diagnosis?

• A Central diabetes insipidus ✓
• B Nephrogenic diabetes insipidus
• C Primary polydipsia
• D Syndrome of inappropriate antidiuresis

Explanation

B rise in urine osmolality of more than 50 percent after desmopressin indicates vasopressin deficiency, confirming central diabetes insipidus, a recognised complication of pituitary surgery. In nephrogenic diabetes insipidus the kidney cannot respond, so desmopressin produces little or no rise. Primary polydipsia shows appropriate concentration with water deprivation rather than this pattern.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.