Serotonin syndrome

• Serotonin syndrome is a potentially life-threatening disorder due to increased serotonergic activity in the central nervous system, characterised by:

  • Altered mental status
  • Autonomic hyperactivity
  • Neuromuscular abnormalities
• Causes:

  • Most commonly an SSRI
  • SNRI
  • MAOI
  • TCA
  • Tramadol - synthetic opiate with serotonergic effects
  • St John Wort
  • Stimulants - MDMA, LSD, cocaine
• Symptoms:

  • Altered mental status - may present as anxiety, restlessness, disorientation, or agitation
  • Sweating
  • Fever
  • Vomiting
  • Diarrhoea
• Signs:

  • Dilated pupils
  • Flushed skin, diaphoresis
  • Tachycardia
  • Hypertension
  • Hyperthermia
  • Hyperreflexia
  • Clonus
  • Myoclonus
  • Rigidity (not lead pipe rigidity like in NMS)
  • Babinski sign positive
• Hyperreflexia and clonus are particularly important and often specific signs
• Investigations are not required for the diagnosis, but may help to rule out other suspected conditions. In serotonin syndrome, there may be:

  • Increased WCC
  • Increased CK
• Management is to stop the offending drugs and supportive care

  • Mild cases - most resolve within 72 hours of stopping the drugs
  • Severe cases - may require ICU admission - main indication is hyperthermia (e.g. >40) - should be treated aggressively
  • The antihistamine Cyproheptadine may be used due to its serotonin-antagonistic effects
• Potential complications:

  • Severe hyperthermia
  • Rhabdomyolysis
  • ARDS
  • DIC
  • Seizures
  • Renal failure
  • Severe hypertension
• Usually occurs with higher doses of antidepressants and when multiple antidepressants are used together