Which option best captures the essence of dilutional hyponatremia?

• A. Water poisoning leading to brain edema and potential death
• B. Excess sodium intake
• C. Dehydration with hyposmolality
• D. Increased serum potassium

Answer: (A)

Dilutional hyponatremia occurs when there is too much free water relative to sodium, so the blood becomes diluted and the serum sodium falls. The extracellular fluid becomes hypotonic, which drives water into cells, including brain cells, leading to cerebral edema. This swelling of brain tissue can cause severe symptoms and, if severe or rapid, can be life-threatening. Saying it as water overload that dilutes sodium effectively captures the mechanism and the risk.

Other options don’t fit as well: excess sodium intake would raise serum sodium, not dilute it; dehydration typically concentrates sodium and solutes (not dilutes them) and doesn’t produce dilutional hyponatremia; increased serum potassium is a separate electrolyte disturbance and not the cause of hyponatremia.