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Difficulty: MediumMedical History Evaluation

A 42-year-old woman is brought to the emergency department by her husband due to worsening confusion, unsteadiness, and a prominent tremor over the past three days. Her past medical history is significant for bipolar disorder, which has been well-controlled on lithium carbonate for several years, and chronic migraines. Two weeks ago, she sustained a minor ankle sprain while hiking. Her vital signs are temperature 37.1°C (98.8°F), blood pressure 122/78 mmHg, heart rate 84/min, and respiratory rate 14/min. Physical examination is notable for a coarse resting tremor, bilateral horizontal nystagmus, and an ataxic gait. Eliciting which of the following specific historical details is the most critical next step to establish the etiology of this patient's current presentation?

  1. Recent use of over-the-counter nonsteroidal anti-inflammatory drugsAnswer
  2. B
    Recent dietary consumption of tyramine-rich foods and beverages
  3. C
    Occurrence of a head impact during the recent hiking trip
  4. D
    Adherence to scheduled age-appropriate cardiovascular and metabolic screening
  5. E
    Concurrent initiation of a beta-blocker for migraine prophylaxis

Answer

The correct historical detail to elicit is the recent use of over-the-counter nonsteroidal anti-inflammatory drugs.
The correct answer identifies the need to inquire about over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs). The patient is exhibiting classic signs of acute lithium toxicity (confusion, ataxia, coarse tremor, nystagmus). Lithium has a narrow therapeutic index and is cleared exclusively by the kidneys. Because NSAIDs inhibit renal prostaglandin synthesis, they decrease afferent arteriolar blood flow, which in turn decreases the glomerular filtration rate and enhances the proximal tubular reabsorption of both sodium and lithium. Given her recent ankle sprain, it is highly probable she began taking OTC ibuprofen or naproxen, precipitating this toxicologic emergency.

Step-by-Step Solution

1
Analyze the patient's acute clinical presentation.
The patient presents with confusion, ataxia, bilateral horizontal nystagmus, and a coarse tremor.
Identifying the clinical syndrome restricts the differential diagnosis. This specific constellation of neurological symptoms in a patient taking lithium is the classic presentation of acute lithium toxicity.
2
Identify potential precipitating factors from the recent history.
The patient sustained a minor ankle sprain while hiking two weeks ago.
Patients frequently self-medicate for minor musculoskeletal injuries with over-the-counter analgesics, providing a critical context clue for a potential drug interaction.
3
Correlate the precipitating event with the suspected diagnosis (lithium toxicity).
Nonsteroidal anti-inflammatory drugs (NSAIDs) are a primary treatment for sprains and are known to drastically reduce the renal clearance of lithium.
Lithium has a narrow therapeutic index. NSAID-induced inhibition of renal prostaglandins decreases glomerular filtration rate and increases proximal tubular reabsorption of lithium, directly causing the toxicity.

Key Concept

Taking a thorough medication history, specifically inquiring about recent over-the-counter NSAID use, is critical when evaluating a patient with signs of lithium toxicity following a musculoskeletal injury.
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Topics

Medical History Evaluation

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