Medical MCQ - 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?

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

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Correct Answer:

syndrome of inappropriate antidiuretic hormone (SIADH) production

Description:

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.

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