A 45-year-old man with chronic alcoholism presents with serum Na⁺ 108 mEq/L, plasma osmolality 230 mOsm/kg, and urine osmolality 80 mOsm/kg. His urine sodium is 10 mEq/L. He is euvolemic on examination. Which condition best explains these findings?
- A SIADH
- B Psychogenic polydipsia
- C Beer potomania ✓
- D Cerebral salt wasting
Correct answer: C. Beer potomania
Explanation
Beer potomania causes hyponatremia with inappropriately dilute urine (80 mOsm/kg) because very low solute intake (low protein, low salt from excessive beer) limits the kidney's ability to excrete free water despite normal diluting capacity. Urine osmolality is low (not maximally dilute but low), and urine sodium is low. SIADH would show concentrated urine (>100 mOsm/kg, typically >300). Psychogenic polydipsia also gives dilute urine but usually with even lower values and a compatible history.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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