NMS — MRCPsych Paper B MCQ

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ModerateSchizophrenia & PsychosisNMSMRCPsych Paper B

A 40-year-old woman with schizophrenia has her haloperidol dose rapidly increased. Over the next 48 hours, she develops confusion, a temperature of 39.8°C, severe generalised muscle rigidity, tachycardia and markedly fluctuating blood pressure. Her creatine kinase is 12,000 IU/L. Her reflexes are normal, with no clonus, and she is not taking a serotonergic medicine. Which syndrome does this describe?

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Correct answer: C — Neuroleptic malignant syndrome

This is neuroleptic malignant syndrome (NMS). The discriminating features are recent haloperidol dose escalation followed by hyperthermia, severe generalised rigidity, altered consciousness, autonomic instability and marked CK elevation from muscle injury. Serotonin syndrome requires relevant serotonergic exposure and more typically produces hyperreflexia and clonus. Malignant catatonia can cause fever and autonomic instability but would usually occur within a catatonic syndrome rather than being closely linked to dopamine-antagonist escalation. Acute dystonia causes focal or generalised sustained contractions but not this systemic syndrome. Delirium accounts for confusion but does not explain profound rigidity and rhabdomyolysis. NMS is a medical emergency: haloperidol should be stopped immediately and urgent supportive medical care and monitoring instituted.

Reference: Electronic Medicines Compendium, Haloperidol 5 mg/ml solution for injection, Summary of Product Characteristics, section 4.4: Neuroleptic malignant syndrome, revised 2025. https://www.medicines.org.uk/emc/product/101458/smpc