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Difficulty: EasyMedical History Evaluation

A 58-year-old man comes to the emergency department reporting a 24-hour history of ringing in his ears, nausea, and vomiting. He also feels that he is breathing more rapidly than usual. His past medical history includes severe osteoarthritis of the knees, hypertension, and a myocardial infarction three years ago. His current prescribed medications are lisinopril, metoprolol, and atorvastatin. Vital signs show a heart rate of 98/min, respiratory rate of 26/min, and blood pressure of 132/82 mm Hg. Physical examination is unremarkable except for tachypnea. Arterial blood gas analysis on room air demonstrates a primary respiratory alkalosis and a primary metabolic acidosis. Which of the following areas of the medical history is most critical to evaluate to establish the etiology of this patient's acute presentation?

  1. Recent use of non-prescription pain relieversAnswer
  2. B
    Recent changes to his prescribed antihypertensive regimen
  3. C
    Recent initiation of a high-protein, low-carbohydrate diet
  4. D
    Concurrent use of herbal supplements containing St. John's wort
  5. E
    Completion status of routine colorectal cancer screening

Answer

Recent use of non-prescription pain relievers
This patient presents with the classic findings of salicylate (aspirin) toxicity: tinnitus, gastrointestinal distress, tachypnea, and a mixed acid-base disorder. Salicylates cause toxicity through two main mechanisms. First, they directly stimulate the medullary respiratory center, leading to hyperventilation and a primary respiratory alkalosis. Second, they uncouple oxidative phosphorylation, resulting in the accumulation of organic acids (e.g., lactic acid, ketoacids) and a primary elevated anion gap metabolic acidosis. Given this patient's history of severe osteoarthritis and the absence of prescribed pain medications on his chart, he is at very high risk for self-medicating with large, toxic doses of over-the-counter aspirin. Therefore, specifically questioning him about his use of non-prescription pain relievers is the most critical component of the medical history evaluation to establish this diagnosis.

Step-by-Step Solution

1
Analyze the patient's acute clinical presentation and laboratory findings.
The patient presents with tinnitus, nausea, tachypnea, and an arterial blood gas showing both a primary respiratory alkalosis and a primary metabolic acidosis.
Identifying the distinct clinical syndrome is the first step in formulating a focused differential diagnosis.
2
Correlate the clinical syndrome with potential etiologies.
The classic triad of tinnitus, hyperventilation (respiratory alkalosis), and high anion gap metabolic acidosis is the hallmark of salicylate toxicity.
Salicylates directly stimulate the medullary respiratory center and simultaneously uncouple oxidative phosphorylation in peripheral tissues.
3
Determine the most appropriate historical question to confirm the suspected diagnosis.
Questioning the patient about non-prescription pain relievers is critical, as he has severe osteoarthritis but no prescribed analgesics, making self-medication with over-the-counter aspirin highly probable.
Patients frequently omit over-the-counter medications from their reported medical history unless specifically asked by the physician.

Key Concept

Establishing a diagnosis of salicylate toxicity by thoroughly evaluating a patient's non-prescription medication history when presenting with classic symptoms (tinnitus, mixed acid-base disorder).
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Topics

Medical History Evaluation

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