A 62-year-old woman is brought to the emergency department by her husband due to progressi… — USMLE Step 2 CK

A $62$ -year-old woman is brought to the emergency department by her husband due to progressive confusion, profound weakness, and mild shortness of breath over the past $3$ days. She has a history of estrogen receptor-positive breast cancer treated with lumpectomy and radiation $4$ years ago. Two months ago, she developed severe back pain and was diagnosed with widespread osteolytic metastases. For the past week, she has been extremely thirsty, urinating frequently, and has not had a bowel movement in $4$ days. Her husband reports she has become increasingly lethargic today.

Vital signs are: temperature $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), pulse $112$ /min, blood pressure $88/55$ mm Hg, and respirations $18$ /min.

Physical examination reveals dry mucous membranes and decreased skin turgor. The lungs are clear to auscultation. Heart sounds are rapid but regular. The abdomen is mildly distended with decreased bowel sounds. Neurologic examination shows a lethargic patient who is oriented to name only.

Laboratory studies show:

Laboratory Test	Result	Reference Range
Hemoglobin	$10.2$ g/dL	$12.0-15.5$ g/dL
Leukocytes	$7,500$ /mm $^3$	$4,500-11,000$ /mm $^3$
Sodium	$148$ mEq/L	$136-145$ mEq/L
Potassium	$4.1$ mEq/L	$3.5-5.0$ mEq/L
Calcium (total)	$14.8$ mg/dL	$8.4-10.2$ mg/dL
Albumin	$3.5$ g/dL	$3.5-5.5$ g/dL
Creatinine	$2.2$ mg/dL	$0.6-1.1$ mg/dL

Which of the following is the most appropriate initial step in the management of this patient's current condition?

Intravenous infusion of 0.9% normal salineAnswer
B
Intravenous administration of furosemide
C
Administration of piperacillin-tazobactam
D
Non-contrast computed tomography of the head
E
Measurement of serum thyroid-stimulating hormone and free T4

Answer

The most appropriate initial step is the administration of an intravenous infusion of 0.9% normal saline.

The correct answer is the intravenous infusion of

0.9\%

normal saline. This patient is presenting with a hypercalcemic crisis secondary to widespread osteolytic metastases from breast cancer. Severe hypercalcemia (typically

>14

mg/dL) induces nephrogenic diabetes insipidus, leading to polyuria, profound dehydration, and acute kidney injury. This hypovolemia is evidenced by her hypotension, tachycardia, dry mucous membranes, and elevated sodium and creatinine. The absolute first step in managing severe hypercalcemia is aggressive volume resuscitation with isotonic saline (typically at

200-300

mL/hr). This dilutes the serum calcium, restores the glomerular filtration rate (GFR), and increases the renal excretion of calcium. Once the patient is euvolemic, long-term treatments such as bisphosphonates (e.g., zoledronic acid) or calcitonin can be safely administered.

Step-by-Step Solution

Identify the primary medical emergency from the clinical presentation and laboratory data.

The patient has severe hypercalcemia (

14.8

mg/dL) due to osteolytic metastases from breast cancer, complicated by severe dehydration and acute kidney injury.

Hypercalcemia causes nephrogenic diabetes insipidus, leading to massive polyuria, polydipsia, volume depletion, and subsequent acute kidney injury (creatinine

2.2

mg/dL) and hypotension.

Determine the priority of interventions for severe hypercalcemia of malignancy.

Immediate intravascular volume expansion must precede all other therapies.

Volume expansion with isotonic saline restores the glomerular filtration rate (GFR), dilutes serum calcium, and promotes the renal excretion of calcium.

Key Concept

The initial management of severe hypercalcemia of malignancy always begins with aggressive intravenous hydration using isotonic saline to restore intravascular volume and promote renal calcium excretion.

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