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Lewy body dementia antipsychotic sensitivity — MRCPsych Paper A MCQ

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HardPsychopharmacologyLewy body dementia antipsychotic sensitivityMRCPsych Paper A

A 74-year-old man has an 18-month history of progressive cognitive impairment, recurrent well-formed visual hallucinations, marked fluctuations in attention and spontaneous bradykinesia and rigidity. His wife also describes dream-enactment behaviour. After a single 0.5 mg oral dose of haloperidol for distressing hallucinations, he develops profound generalised rigidity, immobility, dysphagia and worsening confusion. During the following 24 hours he remains afebrile, with stable blood pressure and pulse, normal serial creatine kinase measurements and no evidence of infection. Which diagnosis best explains this deterioration?

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Correct answer: E — Lewy body dementia antipsychotic sensitivity

The correct answer is E. Cognitive fluctuation, recurrent well-formed visual hallucinations, spontaneous parkinsonism and probable REM sleep behaviour disorder strongly indicate dementia with Lewy bodies. People with this condition may develop profound worsening of rigidity, immobility, swallowing and consciousness after even a small dose of a dopamine-blocking antipsychotic. NICE specifically warns of severe antipsychotic sensitivity reactions, and the haloperidol SmPC contraindicates its use in dementia with Lewy bodies. Neuroleptic malignant syndrome is the closest distractor, but persistent absence of fever, autonomic instability and creatine kinase elevation makes it less likely. Serotonin toxicity would require serotonergic exposure and usually causes clonus and hyperreflexia. The negative infection assessment and close temporal relationship to haloperidol argue against infection-associated delirium. Alcohol withdrawal typically causes tremor, autonomic hyperactivity and a relevant dependence history.

Reference: National Institute for Health and Care Excellence. Dementia: assessment, management and support for people living with dementia and their carers (NG97), recommendation 1.7.4. Published 2018; last reviewed 24 October 2025. https://www.nice.org.uk/guidance/ng97/chapter/Recommendations