Serotonin syndrome
Excess central serotonergic activity produces neuromuscular excitation, autonomic instability and altered mental state within hours, and the muscle activity itself generates the hyperthermia that kills.
Definition
Serotonin toxicity is a drug-induced syndrome of excess central serotonergic activity. It is diagnosed clinically with the Hunter Serotonin Toxicity Criteria, a decision rule validated in overdose populations that requires a serotonergic exposure plus one specific neuromuscular finding. Those findings are spontaneous clonus; inducible or ocular clonus with agitation or diaphoresis; ocular or inducible clonus with hypertonia and fever; or tremor with hyperreflexia. Mild toxicity may not meet the criteria, so they identify the syndrome but do not exclude it.
First principles
Hours after a drug change, not days
Serotonin toxicity follows a serotonergic drug being added, increased, interacted with or taken in overdose. Sixty per cent of cases begin within 6 hours of that change. Most settle within 24 hours of the drug being stopped, and mild cases within 24 to 48 hours. Neuroleptic malignant syndrome, the mimic that matters most, takes days. The drug history and the clock discriminate better than the examination does.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.