UMEM Educational Pearls

Title: Serotonin Syndrome (Part 1) - What is It?

Category: Neurology

Keywords: serotonin syndrome, SSRI, autonomic hyperactivity, hyperreflexia, clonus, Hunter Criteria (PubMed Search)

Posted: 9/9/2015 by WanTsu Wendy Chang, MD
Click here to contact WanTsu Wendy Chang, MD

Serotonin Syndrome - What is It?

Potentially life-threatening condition associated with increased serotonergic activity in the CNS.
Selective serotonin reuptake inhibitors (SSRIs) are the most commonly implicated class of medications. However, other medications can also be involved.
It is a clinical diagnosis!
Classic triad: mental status change, autonomic hyperactivity, and neuromuscular abnormalities
- Mental status change - anxiety, agitation, restlessness, disorientation
- Autonomic hyperactivity - diaphoresis, tachycardia, hypertension, hyperthermia, nausea, vomiting, diarrhea
- Neuromuscular abnormalities - tremor, muscle rigidity, myoclonus, hyperreflexia, clonus, Babinski sign (abnormal plantar reflex)
Hunter Criteria is the most accurate diagnostic rule:
- Serotonergic agent + one of the following:
  - Spontaneous clonus
  - Inducible clonus + agitation or diaphoresis
  - Ocular clonus + agitation or diaphoresis
  - Tremor + hyperreflexia
  - Hypertonia + temperature above 38C + ocular clonus or inducible clonus
Majority of cases present within 24 hours, most within 6 hours, of a change in dose or initiation of a medication.

** Stay tuned for part 2 on what causes serotonin syndrome **

Boyer EW, Shannon M. The serotonin syndrome. N Engl J Med. 2005;352:1112-1120.
Dunkley EJ, Isbister GK, Sibbritt D, Dawson AH, Whyte IM. The Hunter Serotonin Toxicity Criteria: simple and accurate diagnostic decision rules for serotonin toxicity. QJM. 2003;96(9):635.

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