Fast Five Quiz: Serotonin Syndrome

Richard H. Sinert, DO


June 04, 2021

Differentiating serotonin toxicity from other syndromes that have similar manifestations may be difficult. Such syndromes include, but are not limited to, neuroleptic malignant syndrome; malignant hyperthermia; anticholinergic toxicity; and infectious diseases, such as meningitis and encephalitis (Table).

Table. Differentiation of Serotonin Syndrome From Similarly Presenting Conditions

Clinical Feature Serotonin Syndrome Anticholinergic Toxidrome Neuroleptic Malignant Syndrome Malignant Hyperthermia
Medication history Serotoninergic drug Anticholinergic agent Dopamine agonist Inhalational anesthetic
Average onset time < 12 h < 12 h 1-3 d 0.5-24 h
Vital signs Hypertension, tachycardia, tachypnea, fever (>105.8 °F [41 °C]) Hypertension, tachypnea, tachycardia, fever (<102.2 °F [39 °C]) Hypertension, tachycardia, tachypnea, fever (>105.8 °F [41 °C]) Hypertension, tachycardia, tachypnea, hyperthermia
Pupils Mydriasis Mydriasis Normal Normal
Bowel sounds Hyperactive Decreased or absent Normal or decreased Decreased
Tone Increased in lower extremities Normal "Lead-pipe" rigidity in all muscle groups Rigor mortis–like rigidity
Reflexes Hyperreflexia clonus Normal Bradyreflexia Hyporeflexia
Mental status Agitation, coma Agitation, delirium Stupor, alert, mutism, coma Agitation
Adapted from Boyer EW, Shannon M. N Engl J Med. 2005;352:1112-1120.

Read more about the differential diagnoses of serotonin syndrome.


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