Syndrome of inappropriate antidiuresis and cerebral salt wasting syndrome: are they different and does it matter?

The syndrome of inappropriate antidiudresis (SIAD) and cerebral salt wasting (CSW) are similar conditions with the main difference being the absence or presence of volume depletion. The two conditions may be indistinguishable at presentation, as volume status is difficult to assess, which can lead to under-diagnosis of CSW in patients with central nervous system (CNS) disease. Carefully conducted studies in patients with CNS disease have indicated that CSW may be more common than SIAD. CSW may be differentiated from SIAD based on the persistence of hypouricemia and increased fractional excretion of urate following the correction of hyponatremia. Hyponatremia should be prevented if possible and treated promptly when discovered in patients with CNS disease as even mild hyponatremia could lead to neurological deterioration. Fluid restriction should not be used for the prevention or treatment of hyponatremia in hospitalized patients with CNS disease as it could lead to volume depletion especially if CSW is present. 0.9% sodium chloride may not be sufficiently hypertonic for the prevention of hyponatremia in hospitalized patients with CNS disease and a more hypertonic fluid may be required. The preferred therapy for the treatment of hyponatremia in patients with CNS disease is 3% sodium chloride.