Electrolyte Disorders USMLE Step 1 Practice Question
A 78-year-old man with metastatic prostate cancer presents to the emergency department 2 days after initiating chemotherapy with complaints of severe muscle weakness, diffuse cramping, and paresthesias. His wife reports he has had minimal urine output since yesterday. Vital signs: BP 142/88 mmHg, HR 92 bpm, RR 18, Temp 37.2°C, SpO2 98% on room air. Laboratory studies show: Serum calcium: 6.2 mg/dL (normal albumin 4.1 g/dL)
Phosphate: 5.8 mg/dL
Potassium: 6.8 mEq/L
Creatinine: 2.4 mg/dL (baseline 0.9)
Uric acid: 12.5 mg/dL
PTH: 380 pg/mL (normal 15-65)
Alkaline phosphatase: normal Electrocardiography shows peaked T waves. Which of the following best explains this clinical presentation?
Answer choices
- ATumor lysis syndrome with secondary hyperphosphatemia and hypocalcemiaCorrect answer
- BPrimary hyperparathyroidism exacerbated by chemotherapy-induced renal dysfunction
- CVitamin D deficiency from decreased sun exposure during cancer treatment
- DOsteoblastic metastases with increased bone turnover and calcium sequestration
- EHypoalbuminemia from hepatic metastases causing decreased serum calcium binding
- FAcute pancreatitis from chemotherapy with fat necrosis and calcium chelation
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