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Severe Li Toxicity — MRCPsych Paper B MCQ

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EasyMood DisordersSevere Li ToxicityMRCPsych Paper B

A patient receiving maintenance lithium has a 12-hour serum lithium concentration of 2.3 mmol/L. They have repeated vomiting, a coarse tremor, confusion and gait ataxia. Which is the most appropriate interpretation?

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Correct answer: E — Severe lithium toxicity requiring emergency hospital management

The answer is E. A 12-hour lithium concentration of 2.3 mmol/L is clearly toxic, and the combination of vomiting, coarse tremor, confusion and particularly gait ataxia indicates clinically serious neurotoxicity. Ataxia is a cerebellar sign, which the SmPC classifies among severe manifestations. Lithium must be stopped and the patient requires emergency medical assessment, serial lithium levels, renal function and electrolyte testing, ECG monitoring, rehydration and specialist toxicology advice. Haemodialysis is considered for severe poisoning or marked neurological features; it is not determined by a simplistic serum threshold alone. Mild adverse effects more typically include nausea or a fine tremor without confusion or ataxia. A correctly timed 12-hour level excludes a simple sampling-timing explanation.

Reference: Essential Pharma, Lithium Carbonate Essential Pharma 250 mg film-coated tablets, Summary of Product Characteristics, sections 4.4 and 4.9, text revised 2024. https://www.medicines.org.uk/emc/product/10828/smpc