How is neuroleptic malignant syndrome different from serotonin syndrome?

• A. NMS has rigidity and slow onset; serotonin syndrome has hyperreflexia and fast onset
• B. NMS has hyperreflexia; serotonin syndrome has rigidity
• C. NMS is not life-threatening; serotonin syndrome is
• D. NMS occurs after antidepressants; serotonin after antipsychotics

Answer: (A)

The key idea is that these two syndromes have different neuromuscular signs and different times of onset, tied to the drugs that usually trigger them. Neuroleptic malignant syndrome (NMS) comes from dopamine-blocking antipsychotics and typically develops over hours to days. It is characterized by severe, “lead-pipe” rigidity and often little movement (hyporeflexia), along with high fever and autonomic instability. Serotonin syndrome, caused by excess serotonin from serotonergic medications, usually appears more rapidly—often within hours of starting or increasing the dose—and shows neuromuscular hyperactivity such as tremor, myoclonus, and especially hyperreflexia with clonus.

So, the best way to distinguish them clinically is: NMS presents with rigidity and a slower onset, whereas serotonin syndrome presents with hyperreflexia and a faster onset. The other statements don’t fit because, for example, NMS can be life-threatening and serotonin syndrome can also be dangerous; their triggers are different (antipsychotics for NMS vs serotonergic drugs for serotonin syndrome), and hyperreflexia is not typical of NMS.