Curriculum · Mental Health / Psychiatry
Serotonin syndrome
What it is
Serotonin syndrome is one of the toxidromes. It is precipitated by serotonergic agents, and follows the ingestion of 2 or more drugs such as MAOIs and SSRIs. Named agonists at the 5HT2A or 5HT1A serotonin receptor include citalopram, ecstasy, tramadol and lithium. Onset is variable but usually under 24 hours, and it is abrupt more often than gradual.
How it presents
The mnemonic HARMED holds the picture:
- Hyperthermia
- Agitation, ANS instability
- Rigidity, Reflexes increased
- Myoclonus, Mydriasis
- Encephalopathy
- Diaphoresis, Diarrhea
The vital signs show HTN, tachycardia, tachypnea and hyperthermia over 40 C; the mucosa shows sialorrhea and the skin diaphoresis; mental status is variable, from an agitated state to coma; muscle tone is increased, particularly in the lower extremities; reflexes show hyperreflexia and clonus; the pupils show mydriasis; and bowel sounds are hyperactive. Mental status changes such as agitation, delirium, confusion and, to a lesser extent, obtundation can develop from the hyperthermia.
One described case is put as a differential diagnosis, not as an answer: a male of 23 treated for psychiatric history was brought in anxious, distressed and confused, with T 38.4 C, PR 130/min, RR 19/min, BP 160/100 mmHg and SpO2 98% on room air, and on examination had shaking eye movements, abnormal tendon reflexes and stiffness of the lower limbs with GCS of 13; autonomic instability, neuromuscular findings and mental status change come together in him, and the four diagnoses to run through are serotonin syndrome, neuroleptic malignant syndrome, anticholinergic syndrome and malignant hyperthermia.
A second described case is serotonin syndrome itself: a female of 25 with major depression on fluoxetine 20 mg daily had paroxetine 10 mg daily added; within a week she reported persistent suicidal ideas, insomnia and constant shaking; the paroxetine was up-titrated over a 3-week period to a dose of 40 mg, and one month later she had extreme fatigue, a heart rate of 135 beat per minute, and uncontrollable twitching, tremor and hyperreflexia.