Serotonin Syndrome — MRCPsych Paper B MCQ

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ModerateLiaison PsychiatrySerotonin SyndromeMRCPsych Paper B

A 40-year-old woman has taken fluoxetine 20 mg daily for 6 months. Tramadol is started for acute pain. Within 24 hours, she develops agitation, a temperature of 39.5°C, profuse diaphoresis, tremor, inducible ankle clonus and generalised hyperreflexia. Which diagnosis best explains this presentation?

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Correct answer: E — Serotonin syndrome

The diagnosis is serotonin syndrome, precipitated by adding serotonergic tramadol to fluoxetine. The rapid onset following the interaction and the combination of agitation, hyperthermia, diaphoresis and neuromuscular hyperactivity—particularly clonus and hyperreflexia—are characteristic. The fluoxetine SmPC specifically warns about serotonin syndrome with tramadol. Neuroleptic malignant syndrome usually follows dopamine-antagonist exposure and is characterised by prominent generalised rigidity rather than clonus and hyperreflexia. Discontinuation syndrome is excluded because fluoxetine has not been stopped. Anticholinergic toxicity typically causes dry skin and mucosa rather than profuse sweating, while hyponatraemia may cause confusion or seizures but does not explain this neuromuscular pattern. Serotonin syndrome is potentially life-threatening and requires urgent medical management.

Reference: electronic Medicines Compendium, Fluoxetine 20 mg Capsules, Summary of Product Characteristics, sections 4.4 and 4.5, updated 2025. https://www.medicines.org.uk/emc/product/13515/smpc