Which of the following is a symptom of serotonin syndrome?

• A. Muscle rigidity
• B. Hypotension
• C. Sedation
• D. Hyporeflexia

Answer: (A)

Excess serotonin in the nervous system causes a hyperactive state that shows up most clearly in the neuromuscular system. Muscle rigidity fits this pattern because the overactive serotonergic signaling increases muscle tone, contributing to stiff, stiffened muscles as part of the overall neuromuscular hyperactivity seen in serotonin syndrome.

Other options don’t align as well with the typical picture. Sedation would suggest reduced CNS arousal, not the agitation and heightened activity common to this syndrome. Hypotension can occur but isn’t a defining neuromuscular finding. Hyporeflexia would contradict the common presence of hyperreflexia and tremor that accompany excess serotonin.