Is it cerebral or renal salt wasting?

Cerebral salt-wasting (CSW), or renal salt-wasting (RSW), has evolved from a misrepresentation of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) to acceptance as a distinct entity. Challenges still confront us as we attempt to differentiate RSW from SIADH, ascertain the prevalence of RSW, and address reports of RSW occurring without cerebral disease. RSW is redefined as 'extracellular volume depletion due to a renal sodium transport abnormality with or without high urinary sodium concentration, presence of hyponatremia or cerebral disease with normal adrenal and thyroid function.' Our inability to differentiate RSW from SIADH lies in the clinical and laboratory similarities between the two syndromes and the difficulty of accurate assessment of extracellular volume. Radioisotopic determinations of extracellular volume in neurosurgical patients reveal renal that RSW is more common than SIADH. We review the persistence of hypouricemia and increased fractional excretion of urate in RSW as compared to correction of both in SIADH, the appropriateness of ADH secretion in RSW, and the importance of differentiating renal RSW from SIADH because of disparate treatment goals: fluid repletion in RSW and fluid restriction in SIADH. Patients with RSW are being incorrectly treated by fluid restriction, with clinical consequences. We conclude that RSW is common and occurs without cerebral disease, and propose changing CSW to RSW.