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Difficulty: MediumMedical History Evaluation

A 44-year-old man is brought to the outpatient clinic by his spouse due to a three-day history of worsening unsteadiness, confusion, and a noticeable hand tremor. He has a history of bipolar disorder that has been well controlled on a stable dose of lithium for the past five years. His other medical conditions include mild essential hypertension and recently diagnosed right knee osteoarthritis. A review of his electronic health record reveals no new prescriptions or dosage changes from his care team over the last six months. His vital signs are within normal limits. On physical examination, he exhibits a coarse bilateral tremor and a broad-based, unsteady gait. Which of the following specific historical inquiries is most critical to establishing the etiology of his current presentation?

  1. Are you taking any over-the-counter nonsteroidal anti-inflammatory drugs for your joint pain?Answer
  2. B
    Have you recently incorporated aged cheeses or cured meats into your diet?
  3. C
    Did you recently start taking a daily low-dose aspirin for cardiovascular protection?
  4. D
    Is there a family history of early-onset movement disorders or dementia?
  5. E
    Have you been taking over-the-counter oral decongestants for a recent cold?

Answer

The most critical inquiry is asking whether the patient has been taking over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) for his joint pain.
The correct answer addresses the need to identify unprescribed medications that interact with the patient's existing regimen. The patient's presentation of confusion, ataxia, and a coarse tremor is highly characteristic of acute-on-chronic lithium toxicity. Lithium has a narrow therapeutic index and is cleared exclusively by the kidneys. Nonsteroidal anti-inflammatory drugs (NSAIDs), which are widely available over-the-counter and frequently used by patients for osteoarthritis, decrease renal prostaglandin synthesis. This reduction leads to afferent arteriolar vasoconstriction, decreased glomerular filtration rate, and significantly decreased renal clearance of lithium. While the electronic health record shows no new prescriptions, querying the patient about recent over-the-counter NSAID use is the most essential step to establish the etiology of his toxic state.

Step-by-Step Solution

1
Analyze the clinical presentation and physical examination findings.
The patient is exhibiting confusion, a broad-based unsteady gait (ataxia), and a coarse hand tremor.
Identifying the primary clinical syndrome is the first step in formulating a differential diagnosis.
2
Correlate the symptom presentation with the patient's past medical and psychiatric history.
The patient has a history of bipolar disorder treated with lithium. The symptoms represent the classic neurologic triad of acute lithium toxicity.
Connecting current symptoms to existing maintenance therapies helps identify adverse drug events or toxicity.
3
Evaluate potential precipitants of toxicity based on the patient's comorbidities.
The patient has recently diagnosed right knee osteoarthritis. Patients frequently self-medicate with over-the-counter medications for new pain.
Since there are no new prescription medications in the electronic health record, an external or unrecorded factor must be responsible.
4
Connect the expected over-the-counter medication with its pharmacokinetic effect on the patient's maintenance therapy.
NSAIDs decrease prostaglandin synthesis, leading to afferent arteriolar vasoconstriction and decreased glomerular filtration rate (GFR). This severely decreases the renal clearance of lithium, leading to toxicity.
Understanding drug-drug interactions is essential for pinpointing the exact historical question needed to confirm the suspected etiology.

Key Concept

Evaluating the medical history for undisclosed over-the-counter medications that interact with narrow therapeutic index drugs.
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Topics

Medical History Evaluation

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