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?

1. A)Syndrome of inappropriate ADH secretionGABARITO
2. B)Psychogenic polydipsia
3. C)Primary hyperaldosteronism
4. D)Excessive loop diuretic use
5. E)Central diabetes insipidus