A 71-year-old man is admitted to the intensive care unit with a 3-day history of worsening… — USMLE Step 3

A 71-year-old man is admitted to the intensive care unit with a 3-day history of worsening confusion, severe weakness, and diffuse abdominal pain with constipation. He has a history of squamous cell carcinoma of the lung with diffuse metastases to the ribs and thoracic spine. The patient has been unable to drink fluids for the past 2 days due to profound nausea. Vital signs show temperature $37.2^\circ\text{C}$ , heart rate $118\text{/min}$ , blood pressure $92/58\text{ mmHg}$ , and respiratory rate $18\text{/min}$ . Physical examination reveals a somnolent patient who withdraws from painful stimuli. His mucous membranes are extremely dry, and skin turgor is significantly decreased.

Initial laboratory studies reveal:
Serum sodium: $148\text{ mEq/L}$
Serum potassium: $4.2\text{ mEq/L}$
Serum chloride: $106\text{ mEq/L}$
Serum bicarbonate: $24\text{ mEq/L}$
Blood urea nitrogen: $82\text{ mg/dL}$
Serum creatinine: $4.8\text{ mg/dL}$ (baseline $1.2\text{ mg/dL}$ )
Serum total calcium: $16.2\text{ mg/dL}$
Serum albumin: $3.0\text{ mg/dL}$
Serum phosphorus: $2.1\text{ mg/dL}$

Aggressive intravenous hydration with $0.9\%$ normal saline and administration of subcutaneous calcitonin are immediately initiated. Which of the following is the most appropriate additional pharmacologic intervention to provide sustained control of this patient's hypercalcemia?

A
Intravenous zoledronic acid
B
Intravenous furosemide
C
Intravenous hydrocortisone
Subcutaneous denosumabCevap
E
Oral cinacalcet

Cevap

Subcutaneous denosumab is the most appropriate intervention for sustained calcium control because it is not nephrotoxic and can be safely used in the setting of severe acute kidney injury.

The correct answer is subcutaneous denosumab. This patient presents with severe hypercalcemia of malignancy (HCM) and a superimposed acute kidney injury (AKI). The immediate management of severe HCM requires aggressive intravenous isotonic fluid resuscitation to restore intravascular volume and calcitonin for a rapid decline in serum calcium. Because calcitonin's effect is transient (tachyphylaxis occurs within 48 hours), a long-acting bone resorption inhibitor must be administered concurrently. While intravenous bisphosphonates are traditionally first-line for sustained control, they are highly nephrotoxic and contraindicated in patients with severe renal impairment (e.g., serum creatinine

> 4.5\text{ mg/dL}

or CrCl

< 30\text{ mL/min}

). Denosumab is a monoclonal antibody that binds to the receptor activator of nuclear factor kappa-B ligand (RANKL), preventing osteoclast activation. It is not cleared by the kidneys, lacks nephrotoxicity, and is the preferred guideline-supported agent for long-term calcium control in HCM patients with severe AKI.

Adım Adım Çözüm

Determine the severity and etiology of the metabolic derangement.

The patient has severe hypercalcemia of malignancy (corrected calcium = 17.0 mg/dL) driven by squamous cell carcinoma (likely PTHrP-mediated or due to osteolytic bone metastases).

Corrected calcium

> 14\text{ mg/dL}

is a life-threatening emergency requiring immediate multi-modal treatment.

Evaluate the patient's renal function based on laboratory values.

The patient has a severe acute kidney injury (AKI) with a serum creatinine of

4.8\text{ mg/dL}

(baseline

1.2\text{ mg/dL}

), likely prerenal from hypercalcemia-induced nephrogenic diabetes insipidus and poor oral intake.

Renal function strictly dictates which long-term calcium-lowering pharmacotherapies can be safely administered.

Select the appropriate class of medication for sustained calcium control.

A long-acting bone resorption inhibitor must be administered concurrently with rapid-acting agents (fluids and calcitonin).

Calcitonin acts rapidly but exhibits tachyphylaxis within 48 hours, requiring a long-term agent to maintain normocalcemia.

Differentiate between available bone resorption inhibitors based on the patient's AKI.

Intravenous bisphosphonates (e.g., zoledronic acid) are contraindicated due to severe nephrotoxicity. Denosumab (a monoclonal antibody against RANKL) is selected.

Denosumab is cleared via the reticuloendothelial system rather than the kidneys, making it the safest and most effective choice for patients with severe renal impairment.

Anahtar Kavram

In patients with severe hypercalcemia of malignancy complicated by severe renal impairment (e.g., severe AKI or CrCl

< 30\text{ mL/min}

), denosumab is the preferred long-acting bone resorption inhibitor over bisphosphonates, which are nephrotoxic and contraindicated.

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