Lithium Nephrogenic DI — ORE Part 1 MCQ

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HardHuman Disease & Dental ManagementLithium Nephrogenic DIORE Part 1

A patient receiving long-term lithium treatment for bipolar disorder reports marked thirst and passing large volumes of urine. They have dry oral mucosa, and serum sodium is 150 mmol/L. Which diagnosis best explains this presentation?

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Correct answer: D — Lithium-related nephrogenic diabetes insipidus

**A is correct.** Long-term lithium can impair renal responsiveness to arginine vasopressin, causing nephrogenic diabetes insipidus. The resulting inability to concentrate urine produces marked polyuria and, when water replacement is inadequate, dehydration and hypernatraemia; a sodium concentration of 150 mmol/L supports free-water loss. The UK lithium SmPC specifically lists nephrogenic diabetes insipidus, polyuria and polydipsia among renal adverse effects. Primary polydipsia usually produces low or low-normal sodium because of excess water intake. Central diabetes insipidus can also cause polyuria with hypernatraemia, but lithium exposure specifically points to a renal, not pituitary, defect. Diabetic ketoacidosis requires supporting hyperglycaemic and acidotic features. Primary adrenal insufficiency typically causes hyponatraemia rather than hypernatraemia.

Reference: Electronic Medicines Compendium. Lithium Carbonate Essential Pharma 250 mg film-coated tablets: Summary of Product Characteristics, sections 4.4 and 4.8, 2024. https://www.medicines.org.uk/emc/product/10828/smpc