Electrolyte Disorders USMLE Step 1 Practice Question
A 76-year-old man with small cell lung carcinoma is admitted for lethargy and unsteady gait. He is euvolemic on examination. Laboratory studies show sodium 118 mEq/L, serum osmolality 255 mOsm/kg, urine sodium 48 mEq/L, and urine osmolality 610 mOsm/kg. Which of the following is the most likely cause of his electrolyte abnormality?
Answer choices
- ASyndrome of inappropriate ADH secretionCorrect answer
- BPsychogenic polydipsia
- CPrimary hyperaldosteronism
- DExcessive loop diuretic use
- ECentral diabetes insipidus
- FAdrenal insufficiency
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