Cerebral Salt Wasting

Definition

Cerebral salt wasting (CSW) is a condition characterized by renal loss of sodium leading to hyponatremia and concomitant decrease in extracellular fluid volume due to an intracranial disease.

CSW was first described in 1950 by Peters et al. They reported three patients with intracranial disorder exhibiting renal salt wasting. In patients with intracranial disorders, hyponatremia is frequently attributed to syndrome of inappropriate hormone secretion (SIADH). However, CSW is another important entity to consider in such patients. As both the conditions have many similar clinical and laboratory findings, it is important to differentiate between the two conditions. This is crucial because the management of each is fundamentally different, and improper treatment may significantly increase the morbidity and mortality.

In clinical practice, hyponatremia (serum Na ⁺ concentration <136 mEq/L) is the commonest electrolyte abnormality encountered. The incidence of mild hyponatremia (serum Na ⁺ 130–135 mEq/L) is estimated to be approximately 30% and moderate to severe hyponatremia is observed in 7% of hospitalized patients. There are varied causes of hyponatremia such as hormone disorders, medications, volume status of the patient, etc., and thus diagnosis of exact etiology is important for its management.

Etiology

CSW chiefly occurs in patients with subarachnoid hemorrhage (SAH). Other conditions where it has been reported to occur include head injury, brain tumors, brain infarction, intracranial hemorrhage, arteriovenous malformations, meningitis, central nervous system derangements, and intracranial surgeries. In a study by Wijdicks et al., approximately 67% of patients with hyponatremia after SAH (rupture of intracranial aneurysm) had CSW as the etiology for hyponatremia. However, Sherlock et al. found CSW as the cause of hyponatremia in only 6.5% of patients who presented with spontaneous SAH and hyponatremia. Vespa reported CSW in 5–10% of patients with traumatic brain injury. The CSW syndrome can also be associated with status epilepticus. Hence, hydration status and electrolytes should be monitored closely in these patients.