Serotonin syndrome versus neuroleptic malignant syndrome: clonus or lead pipe
SEROTONIN SYNDROME crit | NEUROLEPTIC MALIGNANT SYNDROME crit | |
|---|---|---|
| Trigger | A serotonergic agent added or increased, most often two together: an SSRI or SNRI with a triptan, tramadol, linezolid, St. John's wort, dextromethorphan, or an MAOI | Dopamine blockade: a newly started or increased antipsychotic, or abrupt withdrawal of a dopaminergic drug such as levodopa |
| Onset | Fast, usually within 24 hours of the change | Slower, over days into one to two weeks |
| Muscle tone | Tremor and myoclonus, greater in the lower extremities | Generalized lead-pipe rigidity, uniform through the range of motion |
| Reflexes | Hyperreflexia with clonus, the signature finding, worse in the legs | Decreased, hyporeflexia |
| Pupils | Dilated | Normal |
| Bowel sounds | Hyperactive, with diarrhea | Decreased, with ileus |
| Temperature and autonomic picture | Fever with agitation, diaphoresis, tachycardia, labile blood pressure | High fever with marked autonomic instability, rising creatine kinase, risk of rhabdomyolysis and acute kidney injury |
| First actions | Stop all serotonergic agents; support airway, breathing, and circulation; cool actively; give benzodiazepines for agitation and muscle activity; anticipate cyproheptadine | Stop the antipsychotic; cool actively; hydrate aggressively to protect the kidneys; monitor renal function and creatine kinase; anticipate dantrolene and bromocriptine |
Shared findings that do not help you — fever, altered mental status, and autonomic instability appear in both. Do not spend the item on them.
The one line that separates them
Hyperreflexia with clonus points to serotonin. Rigidity with hyporeflexia points to dopamine blockade.
How the stems are built
Serotonin stems name a recent medication addition and then give you movement: twitching, shivering, restlessness, loose stools. Neuroleptic stems name an antipsychotic started days ago and then give you stillness: a stiff patient, a silent abdomen, a temperature climbing.
Memory hook: HOT and TWITCHY is serotonin. HOT and STIFF is neuroleptic.
Watch outboth are stop-the-drug emergencies, not hold-and-monitor. An option that says to withhold the next dose and continue to observe is wrong in both columns. → BOOK 07 · P8 for creatine kinase and renal values.
Takeawaycheck reflexes and muscle tone before you commit to an answer.