In this episode, I’ll discuss three ways to tell the difference between serotonin syndrome and neuroleptic malignant syndrome.
Muscular rigidity, significant hyperthermia, and autonomic instability are all common features of serotonin syndrome and neuroleptic malignant syndrome. While these two syndromes are very similar in presentation, they can usually be differentiated by looking at three specific things:
1. Onset of symptoms
The onset of serotonin syndrome (SS) is typically rapid, within a 24 hour period. This contrasts with neuroleptic malignant syndrome (NMS) which has a slower onset anywhere from days to weeks.
2. Neuromuscular reflexes
SS is accompanied by neuromuscular hyperreactivity (tremor, hyperreflexia, and myoclonus); NMS is accompanied by sluggish neuromuscular responses (rigidity and bradyreflexia).
3. Medication history
Medications associated with SS are most classes of antidepressants, monoamine oxidase inhibitors, opioids, dextromethorphan, buspirone, and cyclobenzaprine, among others.
Medications associated with NMS are the dopamine blocking agents such as neuroleptic medications (haloperidol, olanzapine, etc…) and antiemetics (metoclopramide, droperidol, proclorperazine, and promethazine). NMS is also seen in patients treated for parkinsonism in the setting of withdrawal of levodopa or dopamine agonist therapy, as well as with dose reductions and when switching from one agent to another.
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