A 32-year-old man passes 6 litres of dilute urine daily and drinks correspondingly large volumes of water. During a controlled water deprivation test his plasma sodium rises to 149 mEq/L and urine osmolality plateaus at 130 mOsm/kg. One hour after subcutaneous desmopressin, urine osmolality rises to 520 mOsm/kg. What is the most appropriate next step?
- A Start oral desmopressin and arrange pituitary MRI ✓
- B Start hydrochlorothiazide with a low-salt diet
- C Stop all fluids and observe for spontaneous correction
- D Measure urinary aquaporin-2 excretion to confirm the diagnosis
Correct answer: A. Start oral desmopressin and arrange pituitary MRI
Explanation
A rise in urine osmolality greater than 50 percent after desmopressin confirms central diabetes insipidus, reflecting deficient vasopressin secretion. Desmopressin replacement is the definitive treatment, and pituitary MRI is indicated to search for a mass lesion such as a craniopharyngioma. Hydrochlorothiazide with salt restriction is the paradoxical therapy for nephrogenic diabetes insipidus, in which desmopressin produces little or no rise.
Reference: Williams Textbook of Endocrinology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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