**3. Controversy over the relative prevalence of RSW and SIADH**

The consistent view among internists and nephrologists is that RSW is a rare entity as compared to neurosurgeons, who consider RSW to be a common disorder. This important controversy exists because of the difficulty with which one syndrome can be differentiated from the other by usual clinical criteria. Because of overlapping clinical parameters such as hyponatremia, concentrated urines with high UNa, hypouricemia, increased FEurate, associations with intracranial diseases and normal renal, thyroid and adrenal function, there is a diagnostic dilemma that must be resolved in order to arrive at an appropriate therapeutic strategy for both syndromes. The only difference on first exposure with the patient is the volume depletion in RSW and increased volume in SIADH. (Bitew et al, 2009; Schwartz et al, 1957) Unfortunately, the clinical assessment of the volume status of nonedematous patients has been regarded as consistently inaccurate by usual clinical criteria. (Chung et al, 1987; Maesaka et al, 1999; Oh & Carroll; 1999; Singh et al, 2002)

We and others have encountered patients with RSW, who became symptomatic while being water-restricted for an erroneous diagnosis of SIADH. (Gutierrez et al ,2007; Maesaka et al, 1990,2007; Wijdicks et al, 1985 ) The common teaching that RSW is a rare clinical entity virtually eliminates its consideration when encountering patients with nonedematous hyponatremia. Because the major diagnostic conundrum rests with the volume status of these patients, we will review volume studies, mainly in neurosurgical patients, and offer strategies by which we can differentiate one syndrome from the other. In our view, the myriad of studies that have been published on cerebral/renal salt wasting, including the original report on cerebral salt wasting, has not adequately supported the diagnosis of RSW and have contributed to misconceptions. We will attempt to identify parameters by which the diagnosis of RSW can be made in order of their priority. We hope this review will provide information that will allow the reader to assess critically the merit of manuscripts on RSW and SIADH.
