Acute dystonic reaction — MRCPsych Paper A MCQ

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ModeratePsychopharmacologyAcute dystonic reactionMRCPsych Paper A

A 19-year-old man who has not previously received antipsychotic medication is given intramuscular haloperidol. Later that evening, he develops painful involuntary rotation of his neck and sustained upward deviation of both eyes. He remains alert and afebrile. What is the most likely adverse effect?

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Correct answer: E — Acute dystonia

The correct answer is **acute dystonia**. The rapid onset after intramuscular haloperidol, painful sustained neck contraction (torticollis), and fixed upward eye deviation (oculogyric crisis) are characteristic. Young men and antipsychotic-naive patients are particularly susceptible. Akathisia causes subjective inner restlessness with an inability to remain still rather than sustained muscle spasms. Tardive dyskinesia typically follows longer antipsychotic exposure and produces repetitive choreiform or oro-bucco-lingual movements. Serotonin toxicity would be expected to cause features such as hyperreflexia, clonus, autonomic disturbance and hyperthermia. Anticholinergic delirium causes confusion, agitation, mydriasis, dry skin and urinary retention rather than focal dystonic posturing.

Reference: Electronic Medicines Compendium. Haloperidol Injection BP 5 mg/ml, Summary of Product Characteristics, section 4.4: Extrapyramidal symptoms. Updated 2024. https://www.medicines.org.uk/emc/product/514/smpc