A 78-year-old man with Lewy body dementia develops worsening agitation and visual hallucinations. A junior resident prescribes haloperidol 2 mg IM. Three hours later the patient develops severe rigidity, obtundation, and autonomic instability. The most likely explanation is:

• A The patient has developed neuroleptic malignant syndrome secondary to dopamine depletion in the basal ganglia
• B Haloperidol caused serotonin syndrome by blocking serotonin reuptake in Lewy body pathology
• C Lewy body dementia patients have extreme neuroleptic sensitivity; typical and even atypical antipsychotics can cause fatal reactions characterised by parkinsonism, sedation, and autonomic instability ✓
• D Anticholinergic toxicity from haloperidol crossed the blood-brain barrier in an elderly patient

Explanation

Lewy body dementia (DLB) patients have documented severe neuroleptic sensitivity — a hallmark feature of DLB — occurring in up to 50% of cases. Due to severe dopaminergic neuronal loss with alpha-synuclein Lewy bodies, even low-dose typical antipsychotics (haloperidol, chlorpromazine) and many atypicals can cause life-threatening reactions: irreversible parkinsonism, sedation, autonomic instability, and increased mortality. Quetiapine (low-dose) or clozapine are the preferred options if antipsychotics are absolutely necessary. This is not NMS (which requires fever as a cardinal feature).

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.