Cerebral salt wasting is distinguished from SIADH by which volume status feature?

• A. Hypervolemia
• B. Hypovolemia
• C. Normal volume with edema
• D. Volume status is not relevant

Answer: (B)

Cerebral salt wasting causes loss of sodium and water in the kidneys after brain injury, leading to depletion of the extracellular fluid volume. That hypovolemia is the key feature that sets it apart from SIADH, where patients are typically euvolemic (or only mildly hypervolemic) despite hyponatremia. Recognizing this difference matters because treatment differs: cerebral salt wasting requires volume repletion and salt replacement, whereas SIADH is managed mainly with fluid restriction. Therefore, the volume status finding you’d expect in cerebral salt wasting is hypovolemia. Hypervolemia would point toward SIADH rather than CSW, normal volume with edema contradicts the typical hypovolemia, and stating that volume status is not relevant misses the essential distinction.