<prompt> 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 mEqL and osmolality 550 mOsmkg. Which of the following is the most likely diagnosis?nephrotic syndromesyndrome of inappropriate antidiuretic hormone SIADH productionrenal metastases from lung cancerlung metastases from hypernephroma  <response>: The urine osmolality in patients with SIADH need not be hypertonic to plasma, but only inappropriately high compared with serum. The major characteristics of SIADH include hyponatremia, volume expansion without edema, natriuresis, hypouricemia, and normal or reduced serum creatinine level, with normal thyroid and adrenal function. 