Hyponatraemia in a neurosurgical patient: syndrome of inappropriate antidiuretic hormone secretion versus cerebral salt wasting

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Abstract
Hyponatraemia is a common electrolyte disorder in the setting of central nervous system disease and is often attributed to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). This syndrome is characterized by hyponatraemia with an inappropriately concentrated urine, increased urine sodium concentration, and evidence of normal or slightly increased intravascular volume. By contrast, there are patients with intracranial disease who develop hyponatraemia with similar characteristics but differ in that there is clinical evidence of a contracted extracellular fluid (ECF) volume. This form of hyponatraemia is due to excessive renal sodium excretion resulting from a centrally mediated process and is termed cerebral salt wasting (CSW). While fluid restriction is the treatment of choice in SIADH, the treatment of CSW consists of vigorous sodium and volume replacement. Given the divergent nature of the treatment and the potential for improper selection of fluid therapy to worsen the underlying clinical condition it is of paramount importance for the clinician to be able to recognize and differentiate between these two entities.