Table 2

Comparison of serotonin syndrome, neuroleptic malignant syndrome (NMS), and neuroleptic malignant-like syndrome (NMLS)

Serotonin syndromeNMLSNMS
Onset<12 h>24 h>24 h
PrecipitantSerotonergic drugs*Withdrawal of PD drugsNeuroleptics
Clinical differentiatorsAgitation (drowsiness in advanced stages) Hypereflexia/myoclonusDiarrhoeaMydriasis
  • Dysphagia

  • Hypersalivation

  • Akinesia

Clinical commonalities
  • Hyperthermia

  • Altered mental status

  • Hyperthermia

  • Dysautonomia

  • Rigidity

Pathological findings
  • Leucocytosis

  • Raised creatinine kinase

  • Myoglobinuria

  • Metabolic acidosis

General treatment measures
  • Airway management

  • Respiratory support

  • Fluid management

  • Renal support

Specific treatment
  • Stop serotonergic medications

  • Cyproheptadine

  • Chlorpromazine

  • Benzodiazepines

Dopaminergic medications
  • Stop neuroleptics

  • Dopamine agonists

  • Dantrolene

  • * MAOI, monoamine oxidase inhibitor; SSRI, selective serotonin reuptake inhibitor. (Opiates may potentiate the serotonergic effects of these drugs).