Which of the following is a severe feature of serotonin syndrome?

• A. Tremor
• B. Diarrhea
• C. Muscle rigidity and fever
• D. Seizures

Answer: (C)

Serotonin syndrome can range from mild neurologic symptoms to a life-threatening state marked by intense neuromuscular activity and high fever. The hallmark of a severe form is the combination of pronounced muscle rigidity and hyperthermia. When muscles are rigid, they continuously contract, generating heat and risking rhabdomyolysis, metabolic collapse, and organ failure if not addressed promptly. While tremor and diarrhea are common and can appear early, they usually indicate milder involvement and do not alone signal a severe course. Seizures can occur but are not as defining of severity as the presence of rigid muscles paired with fever. In severe cases, treatment focuses on stopping the triggering medications, aggressive cooling, IV fluids, and agents like benzodiazepines to lessen muscle activity, with specific antidotes considered as needed.