Electrolyte Disorders — Hyponatremia

A 62-year-old man with small-cell lung cancer presents with confusion and lethargy. Serum sodium is 118 mEq/L. What is the most common cause of hyponatremia in this clinical setting?

A 62-year-old man with small-cell lung cancer presents with confusion and lethargy. Serum sodium is 118 mEq/L, serum osmolality is 245 mOsm/kg, and urine osmolality is 580 mOsm/kg. Which of the following is NOT a recognized mechanism of hyponatremia in this clinical scenario?

A 58-year-old man with small-cell lung cancer presents with hyponatremia (Na+ 118 mEq/L). Urine osmolality is 450 mOsm/kg and urine sodium is 65 mEq/L. Another patient with cirrhosis and ascites has hyponatremia (Na+ 120 mEq/L), urine osmolality 280 mOsm/kg, and urine sodium 15 mEq/L. Which feature best distinguishes SIADH from hyponatremia due to cirrhosis?

A 42-year-old woman on thiazide diuretics for hypertension presents with symptomatic hyponatremia (Na 122 mEq/L). She is euvolemic on examination. Serum osmolality is 250 mOsm/kg and urine osmolality is 580 mOsm/kg. Which investigation would best differentiate thiazide-induced hyponatremia from SIADH?

Which of the following is the primary mechanism by which SIADH (Syndrome of Inappropriate Antidiuretic Hormone) causes hyponatremia?