NMS — MRCPsych Paper B MCQ

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ModerateSchizophrenia & PsychosisNMSMRCPsych Paper B

A 30-year-old man with schizophrenia develops physical symptoms several days after his clozapine dose is increased. His temperature is 39.5°C and he is confused, with generalised muscle rigidity, tachycardia and markedly fluctuating blood pressure. His creatine kinase is 15,000 IU/L. Which is the most likely diagnosis?

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Correct answer: A — Neuroleptic malignant syndrome

Explanation lettering: B = shown as A · C = shown as B · A = shown as C · E = shown as D · D = shown as E

B is the most likely diagnosis. The recent clozapine dose increase followed by hyperthermia, altered consciousness, generalised rigidity, autonomic instability and marked CK elevation is characteristic of neuroleptic malignant syndrome (NMS). Clozapine can cause NMS despite its relatively low propensity to produce extrapyramidal adverse effects. Serotonin syndrome usually follows serotonergic exposure and is more associated with clonus and hyperreflexia. Clozapine-induced myocarditis typically presents with persistent tachycardia, chest pain, dyspnoea or heart-failure symptoms and does not explain the rigidity and severe CK elevation. Malignant hyperthermia requires exposure to triggering anaesthetic agents, while sepsis remains an important exclusion but does not best explain this antipsychotic-associated neuromuscular syndrome. NMS is a medical emergency requiring immediate withdrawal of the antipsychotic and urgent medical treatment.

Reference: Clozaril 100 mg Tablets, Summary of Product Characteristics, sections 4.4 and 4.8, revised February 2026. https://www.medicines.org.uk/emc/product/10290/smpc