Serotonin Syndrome

Summary

Serotonin syndrome is a potentially life-threatening condition caused by excessive serotonin activity.

It can be triggered by herbal supplements like Saint John’s wort, as well as by serotonin-altering drugs like antidepressants.

The clinical features can be grouped into several categories, including autonomic dysfunction—manifesting as fever, sweating, tachycardia, and hypertension. Serotonin syndrome classically causes neuromuscular symptoms -- manifesting as hyperreflexia, myoclonus, increased muscle tone, tremor, and even seizures in severe cases. Gastrointestinal symptoms like diarrhea, nausea, and vomiting are also common, helping distinguish serotonin syndrome from other conditions like neuroleptic malignant syndrome. You’ll also often see mental status changes, including confusion and agitation.

Treatment involves serotonin blocking drugs like cyproheptadine, along with supportive care using benzodiazepines to control agitation and other symptoms.

Key Points

• Serotonin Syndrome
  • Definition
    • Potentially life-threatening syndrome caused by buildup of serotonin
  • Causes
    • Caused by concurrent use of medications/supplements that increase serotonin levels
    • Antidepressants
      • SSRIs
      • SNRIs
      • MAOIs
      • Buspirone
    • St John's Wort
  • Clinical Features
    • Increased neuromuscular activity
      • Hyperreflexia
        • This is a key differentiating factor vs. NMS (which has decreased reflexes)
      • Myoclonus (muscle jerks)
        • This is a key differentiating factor vs. NMS (which is characterized by muscle rigidity instead of jerking)
      • Tremor
        • Restlessness
      • Increased muscle tone
      • Seizures
    • Autonomic dysfunction
      • Fever
      • Sweating (diaphoresis)
      • Tachycardia
      • Hypertension
    • GI symptoms
      • Diarrhea
        • The presence of GI symptoms (e.g. serotonin effects on gut) is key differentiator vs. NMS
      • Nausea/Vomiting
    • Altered mental status
      • Agitation
      • Confusion
  • Treatment
    • If symptoms are detected, hold the offending medication and notify the provider
    • Benzodiazepines
    • Cyproheptadine
      • A serotonin antagonist