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Difficulty: MediumMedical History Evaluation

A 65-year-old woman is brought to the emergency department by her son due to a one-week history of worsening confusion, lethargy, and severe constipation. She has also been complaining of increased thirst and frequent urination. Her past medical history is notable for hypertension, osteoporosis, and osteoarthritis of the knees. Her chronic medications include hydrochlorothiazide, amlodipine, and daily ibuprofen. The son reports that she has been experiencing frequent heartburn over the past month and has been self-medicating by consuming large quantities of over-the-counter antacid tablets. On examination, the patient is somnolent but arousable. Mucous membranes are dry.

Initial laboratory studies reveal:
Sodium: 137 mEq/L
Potassium: 3.4 mEq/L
Chloride: 96 mEq/L
Bicarbonate: 35 mEq/L
BUN: 45 mg/dL
Creatinine: 2.2 mg/dL (baseline 0.9 mg/dL)
Calcium: 14.5 mg/dL
Parathyroid hormone (PTH): 8 pg/mL (normal 10-65 pg/mL)

In addition to her recent over-the-counter antacid use, which of the following elements of this patient's medical history most significantly predisposed her to developing this specific acute laboratory presentation?

  1. A
    History of osteoporosis
  2. B
    Daily ibuprofen consumption
  3. C
    Use of amlodipine
  4. Use of hydrochlorothiazideAnswer
  5. E
    Advanced age and postmenopausal status

Answer

Use of hydrochlorothiazide
The correct answer identifies that the patient's chronic use of a thiazide diuretic is the key predisposing factor for her condition. The patient has milk-alkali syndrome, characterized by the triad of hypercalcemia, metabolic alkalosis, and acute kidney injury resulting from the massive ingestion of calcium carbonate antacids. Hydrochlorothiazide increases renal calcium reabsorption in the distal convoluted tubule, thereby decreasing urinary calcium excretion. When a patient on a thiazide diuretic consumes large amounts of exogenous calcium, they are unable to adequately excrete the excess load, strongly predisposing them to severe hypercalcemia and subsequent renal impairment.

Step-by-Step Solution

1
Analyze the clinical presentation and laboratory findings.
The patient presents with the classic triad of hypercalcemia, metabolic alkalosis, and acute kidney injury, alongside a suppressed parathyroid hormone level.
Identifying this triad in the context of massive antacid (calcium carbonate) ingestion establishes the diagnosis of milk-alkali syndrome.
2
Evaluate the patient's medical history for predisposing factors.
The patient is chronically taking hydrochlorothiazide for hypertension.
Thiazide diuretics decrease urinary calcium excretion. This pharmacological effect creates a permissive environment for severe hypercalcemia when large amounts of exogenous calcium are ingested.

Key Concept

Milk-alkali syndrome presents with hypercalcemia, metabolic alkalosis, and acute kidney injury due to excessive ingestion of calcium and absorbable alkali. Concurrent use of thiazide diuretics is a major predisposing factor because they decrease renal calcium excretion.
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Topics

Medical History Evaluation

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