A 77-year-old man with a mass in the lung develops asymptomatic hyponatremia. His JVP is 4 cm, heart sounds are normal, and the lungs are clear. The urine sodium is 64 mEq/L and osmolality 550 mOsm/kg. Which of the following is the most likely diagnosis?
nephrotic syndrome syndrome of inappropriate antidiuretic hormone (SIADH) production renal metastases from lung cancer lung metastases from hypernephroma