Which of the following conditions is not associated with hyponatremia?

• A. Addison disease
• B. Diarrhea
• C. Diuretic therapy
• D. Cushing syndrome

Answer: (D)

Hyponatremia occurs when there is too much free water relative to sodium in the body, often from increased ADH activity, loss of sodium, or dilution. Addison disease leads to hyponatremia because aldosterone deficiency causes salt wasting and volume depletion, which stimulates ADH and dilutes serum sodium. Diarrhea also lowers serum sodium by causing loss of sodium (and water) from the gut, sometimes accompanied by volume depletion that drives more ADH release. Diuretic therapy, especially thiazides, promotes sodium loss in the urine and can lead to dilutional hyponatremia.

Cushing syndrome does not typically cause hyponatremia; excess cortisol tends to promote sodium retention and can raise blood pressure, so hyponatremia is not a common feature.