Expansion
Autonomic, neuromuscular and mental state changes, with clonus
Expansion
The triad
- Autonomic: hyperthermia, sweating, tachycardia, hypertension, diarrhoea, mydriasis
- Neuromuscular: clonus, the most specific sign, hyperreflexia, tremor, myoclonus, all worse in the lower limbs
- Mental state: agitation, confusion, anxiety
Onset is rapid, usually within 24 hours of a new drug or dose increase.
Causative combinations: SSRIs or SNRIs with tramadol, linezolid, MAOIs, triptans, St John’s wort, ondansetron, lithium, amphetamines or methylene blue.
| Serotonin syndrome | Neuroleptic malignant syndrome | |
|---|---|---|
| Onset | Hours | Days to weeks |
| Drug | Serotonergic | Dopamine antagonist, or dopamine withdrawal |
| Tone | Clonus, hyperreflexia | Lead pipe rigidity |
| Pupils | Dilated | Normal |
| Bowel sounds | Increased | Normal or reduced |
| Resolution | 24 to 72 hours | Days to weeks |
“Serotonin is fast and jerky; neuroleptic malignant is slow and stiff.”
Treatment: stop the drug, benzodiazepines for agitation and rigidity, active cooling, fluids, and cyproheptadine if severe. Watch for rhabdomyolysis, renal failure and DIC.