USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which group of symptoms characterizes serotonin syndrome?

1. Hypertension and bradycardia

2. Bradypnea and hypotension

3. Clonus and hyperreflexia

4. Tonic-clonic seizures and coma

The correct answer is: Clonus and hyperreflexia

Serotonin syndrome is a potentially life-threatening condition that occurs due to an excess of serotonin in the central nervous system, often as a result of medication interactions, overdose, or the use of drugs that increase serotonin levels. The hallmark symptoms of serotonin syndrome include alterations in mental status, autonomic instability, and neuromuscular abnormalities. The presence of clonus and hyperreflexia is particularly characteristic of serotonin syndrome. Clonus refers to the rapid, rhythmic contractions and relaxations of a muscle or group of muscles, typically elicited by a quick stretch of the muscle. Hyperreflexia, on the other hand, is an exaggerated response to stimuli as seen in reflex testing. These neuromuscular findings result from increased excitability of the spinal cord due to elevated levels of serotonin. While the other symptoms mentioned in the question could be associated with different medical conditions, they do not specifically define serotonin syndrome. For instance, bradycardia and hypotension are more aligned with issues like opioid overdose or certain types of shock, while tonic-clonic seizures and coma are indicative of severe neurological disturbances typically not limited to serotonin excess. Therefore, clonus and hyperreflexia stand out as definitive signs of serotonin syndrome.