Serotonin syndrome features: Which of the following symptom clusters is most characteristic?

• A. Aggression and lethargy.
• B. Bradycardia and hypotension.
• C. Agitation, neuromuscular hyperactivity (hyperreflexia), and autonomic instability.
• D. Weight gain and edema.

Answer: (C)

Serotonin syndrome occurs from excessive serotonin activity, usually due to interactions or high doses of serotonergic drugs. The most characteristic features come in three interconnected domains: mental status changes (such as agitation or confusion), autonomic instability (including tachycardia, hypertension, sweating, sometimes fever), and neuromuscular hyperactivity (notably hyperreflexia and clonus). This combination—agitation with clear neuromuscular hyperactivity and autonomic signs—best captures the syndrome’s classic presentation. Other clusters don’t fit as well because they miss the distinctive neuromuscular and autonomic patterns; for example, aggression and lethargy don’t reflect the hyperactivity and autonomic fluctuations, bradycardia and hypotension run opposite the usual autonomic signs, and weight gain with edema aren’t acute manifestations of a serotonin crisis. Recognizing this triad helps differentiate serotonin syndrome from other causes of agitation or autonomic disturbance.