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Difficulty: MediumMedical History Evaluation

An ambulatory care physician is seeing a 28-year-old man who complains of severe restlessness, uncontrollable shivering, and a "racing heart" that began 24 hours ago. His past psychiatric history is notable for generalized anxiety disorder and major depressive disorder, which have been well controlled on paroxetine for the past three years. He has no other chronic medical conditions. Vital signs show a temperature of 38.4°C (101.1°F), blood pressure of 158/92 mmHg, pulse of 115/min, and respirations of 18/min. On physical examination, the patient is visibly diaphoretic and tremulous. Neurologic examination reveals prominent hyperreflexia and bilateral inducible ankle clonus. Point-of-care laboratory testing reveals a mild leukocytosis of 11,500/mm³. The physician suspects a specific toxidrome and begins a targeted medical history evaluation. Which of the following historical elements is most likely responsible for this patient's current condition?

  1. Initiation of an over-the-counter cough suppressant containing dextromethorphanAnswer
  2. B
    Consumption of imported aged cheeses and red wine
  3. C
    Abrupt discontinuation of a nightly lorazepam dose
  4. D
    Concomitant use of a nonsteroidal anti-inflammatory drug for muscle pain
  5. E
    Recent exposure to a coworker with a confirmed respiratory infection

Answer

Initiation of an over-the-counter cough suppressant containing dextromethorphan
The correct answer involves the use of an over-the-counter cough suppressant containing dextromethorphan. This patient is presenting with classic signs of serotonin syndrome, which is characterized by the triad of autonomic instability (tachycardia, hyperthermia, diaphoresis), altered mental status (agitation, restlessness), and neuromuscular hyperactivity (tremor, prominent hyperreflexia, and clonus). Paroxetine is a selective serotonin reuptake inhibitor (SSRI). Dextromethorphan is a commonly used over-the-counter antitussive that also possesses serotonergic properties. When taken concurrently with an SSRI, it can precipitate serotonin syndrome. Thoroughly evaluating the medical history for recent over-the-counter medications is a critical step in establishing this diagnosis.

Step-by-Step Solution

1
Identify the clinical toxidrome based on vital signs and physical examination findings.
The combination of autonomic instability (fever, tachycardia, diaphoresis), altered mental status (restlessness), and neuromuscular hyperactivity (hyperreflexia, clonus) forms the classic triad of serotonin syndrome.
Recognizing the pattern of symptoms is the first step in diagnosing medication-induced toxidromes.
2
Review the patient's current medication list for potential precipitants.
The patient is taking paroxetine, a selective serotonin reuptake inhibitor (SSRI), which provides a baseline elevation in serotonergic tone.
Identifying the baseline medications helps narrow down potential drug-drug interactions that could cause the acute presentation.
3
Evaluate the missing historical elements that could interact with the patient's baseline medication to cause the identified toxidrome.
Dextromethorphan, often found in over-the-counter cough suppressants, acts as a weak serotonin reuptake inhibitor. Its addition to an SSRI is a well-known trigger for serotonin syndrome.
Targeted medical history evaluation for over-the-counter and herbal supplements is critical, as patients frequently omit them unless directly asked.

Key Concept

Eliciting a thorough history of over-the-counter medication use is essential, as agents like dextromethorphan can interact with prescribed SSRIs to precipitate life-threatening serotonin syndrome.
Estimated Time:1m 0s
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Medical History Evaluation

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