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Lithium-Induced Nephrogenic DI — RACP Adult Medicine MCQ

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ModerateNephrologyLithium-Induced Nephrogenic DIRACP Adult Medicine

A 50-year-old man on long-term lithium presents with polyuria (5 L/day), polydipsia, and Na⁺ 148 mmol/L. Urine osmolality is 200 mOsm/kg (dilute). After DDAVP, urine osmolality only rises to 280 mOsm/kg (inadequate response). Lithium level is therapeutic (0.8 mmol/L). What is the most likely cause?

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Correct answer: A — Nephrogenic diabetes insipidus

Polyuria with dilute urine, hypernatraemia, and failure to concentrate urine after DDAVP (rules out central DI) in a patient on lithium is nephrogenic diabetes insipidus. Lithium is the most common drug cause of NDI (affects ~40% of long-term users). It impairs aquaporin-2 expression in collecting ducts. Treatment: adequate fluid access, consider amiloride (reduces lithium entry into collecting duct cells via ENaC), and if possible reduce or cease lithium.

Reference: eTG Endocrine – 2024 – NDI; AMH 2025 Lithium