Which CNS injury complication is most associated with hyponatremia due to natriuresis after brain injury?

Which CNS injury complication is most associated with hyponatremia due to natriuresis after brain injury?

• A. Syndrome of inappropriate antidiuretic hormone (SIADH)
• B. Cerebral salt wasting syndrome
• C. Diabetes insipidus
• D. Spinal shock

Answer: (B)

Hyponatremia after brain injury due to natriuresis points to cerebral salt wasting syndrome. In CSWS, brain injury triggers renal loss of sodium (natriuresis), which drags water with it and leads to a decrease in extracellular fluid volume. This creates hyponatremia with hypovolemia. Urine studies typically show high sodium content and often concentrated urine, while serum osmolality is low. The key treatment is replacing salt and volume (for example, isotonic or even hypertonic saline when needed), rather than restricting fluids. By contrast, SIADH also causes hyponatremia but from inappropriate ADH secretion with euvolemia or slight hypervolemia, not true salt wasting. Diabetes insipidus causes hypernatremia with polyuria and dilute urine, not hyponatremia from natriuresis. Spinal shock isn’t characterized by hyponatremia from natriuresis.

Hyponatremia after brain injury due to natriuresis points to cerebral salt wasting syndrome. In CSWS, brain injury triggers renal loss of sodium (natriuresis), which drags water with it and leads to a decrease in extracellular fluid volume. This creates hyponatremia with hypovolemia. Urine studies typically show high sodium content and often concentrated urine, while serum osmolality is low. The key treatment is replacing salt and volume (for example, isotonic or even hypertonic saline when needed), rather than restricting fluids. By contrast, SIADH also causes hyponatremia but from inappropriate ADH secretion with euvolemia or slight hypervolemia, not true salt wasting. Diabetes insipidus causes hypernatremia with polyuria and dilute urine, not hyponatremia from natriuresis. Spinal shock isn’t characterized by hyponatremia from natriuresis.