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Managing NDI While Continuing Lithium — MRCPsych Paper B MCQ

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HardMood DisordersManaging NDI While Continuing LithiumMRCPsych Paper B

A 60-year-old man with recurrent treatment-resistant unipolar depression has remained well for several years with lithium augmentation. Previous attempts to withdraw lithium were followed by severe depressive relapse despite alternative augmentation strategies. He now has confirmed lithium-induced nephrogenic diabetes insipidus. His serum sodium and potassium are normal, his eGFR is 74 mL/min/1.73 m² and stable, and there is no evidence of lithium toxicity. He can maintain his water intake reliably. Following specialist medical assessment, which management plan is most appropriate?

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Reveal the answer and explanation

Correct answer: B — Continue lithium at the lowest effective level, consider specialist-supervised amiloride, maintain water access, and intensify monitoring

Explanation lettering: D = shown as C · E = shown as D · C = shown as E

B is the best approach. His NDI is currently manageable, renal function and electrolytes are stable, and lithium has uniquely prevented severe depressive relapse. Continuation should therefore be considered through a specialist, individualised benefit–risk assessment rather than automatic withdrawal. Amiloride may be used off-label for lithium-induced NDI because it blocks epithelial sodium channels through which lithium enters collecting-duct principal cells. He should retain unrestricted access to water, with closer monitoring of sodium, potassium, eGFR, lithium concentration and fluid status; amiloride can cause hyperkalaemia and diuretics may alter lithium handling. Immediate discontinuation may become necessary with progressive renal impairment, recurrent hypernatraemia, toxicity or inability to maintain hydration. Valproate is not an equivalent evidence-based substitute for lithium augmentation in unipolar depression. Desmopressin is generally ineffective in nephrogenic DI, and fluid restriction is potentially dangerous. Subtherapeutic lithium sacrifices efficacy without reliably reversing established NDI.

Reference: Schoot TS, Molmans THJ, Grootens KP, Kerckhoffs APM. Systematic review and practical guideline for the prevention and management of the renal side effects of lithium therapy. European Neuropsychopharmacology. 2020;31:16–32. https://pubmed.ncbi.nlm.nih.gov/18596116/