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Hyponatremia from thiazide — USMLE Step 3 MCQ

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HardInternal Medicine (chronic management)Hyponatremia from thiazideUSMLE Step 3

A 74-year-old woman started chlorthalidone 3 weeks ago. She reports fatigue and mild confusion. Sodium is 124 mEq/L, serum osmolality is low, urine osmolality is high, and she appears euvolemic. TSH and morning cortisol are normal. Which of the following is the most likely explanation for this patient's findings?

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Correct answer: D — Thiazide-related impaired urinary dilution

Thiazide diuretics can cause euvolemic hypotonic hyponatremia by impairing renal free-water excretion.

Reference: Hyponatremia expert panel guidance: https://www.kidney.org/