A 19-year-old man has polyuria of 6 L/day and polydipsia. Serum sodium is 149 mEq/L, urine osmolality 105 mOsm/kg during controlled water deprivation. After parenteral desmopressin, urine osmolality rises to 480 mOsm/kg. The most likely diagnosis is:
- A Nephrogenic diabetes insipidus
- B Primary polydipsia
- C Central diabetes insipidus ✓
- D Syndrome of inappropriate antidiuretic hormone secretion
Correct answer: C. Central diabetes insipidus
Explanation
Inability to concentrate urine during water deprivation with a marked rise (more than 50 percent, here well over 300 percent) after desmopressin indicates antidiuretic hormone deficiency, which is central diabetes insipidus. In nephrogenic diabetes insipidus the kidney cannot respond, so desmopressin produces little change, ruling out option A. In primary polydipsia the patient concentrates urine normally once deprived of water, exceeding 800 mOsm/kg, so option B fails.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.