Cerebral salt-wasting syndrome

Cerebral salt-wasting syndrome (CSWS) is a disease featuring hyponatremia (low blood sodium levels) and dehydration in response to disease processes in or surrounding the brain.

Differential diagnosis
It may be difficult to distinguish from the syndrome of inappropriate antidiuretic hormone (SIADH), which develops under similar circumstances and also presents with hyponatremia.

The main clinical difference between these two conditions is that of total fluid status of the patient: CSWS leads to a relative or overt hypovolemia, whereas SIADH is consistent with a normal to hypervolemic patient.

Another useful point in differentiating CSWS from SIADH is a laboratory finding: random urine sodium concentrations tend to be >100 mEq/L in CSWS. SIADH rarely, if ever, leads to a random urine sodium of >100 mEq/L.

Treatment
The reason for the abnormality is different, and treatments are opposites: fluid restriction is used in SIADH, which would worsen cerebral salt wasting. Instead, CSWS is treated with fluids and correction of the low sodium.

Sometimes, fludrocortisone (a mineralocorticoid) improves the hyponatremia.