The Never-Ending Story of Hyponatremia: A Current Problem to Overcome.

: Hyponatremia is a common complication in patients undergoing neurosurgery. If undiagnosed, it has a negative prognostic impact. The two dominant causes of refractory hyponatremia include syndrome of inappropriate ADH secretion (SIADH) and cerebral salt wasting syndrome (CSWS). Discrimination between the two types of disease is not always obvious. We present a case of undiagnosed chronic hyponatremia caused by CSWS after neurosurgery, which not only resulted in a longer hospital stay but also slowed the patient's postoperative recovery. Meticulous clinical evaluation and the performance of appropriate laboratory tests are therefore essential not only for decisive treatment, but also for the establishment of comprehensive diagnostic algorithms that allow timely diagnosis and decisive therapy.

Conclusions: The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and cerebral salt-wasting syndrome (CSWS) are in general associated to refractory hyponatremia especially in patients with neurologic disorders.Extracellular fluid (ECF) assessment is the key to distinguish between SIADH and CSWS.Nevertheless, measurement of the ECF volume is not sufficient to determine the correct etiology and more established diagnostic algorithms are required.