[Hyponatraemia in patients with neurosurgical disorders: SIADH or cerebral salt wasting syndrome?]

Patients with neurosurgical disorders often present with hyponatraemia. Two mechanisms account for hyponatraemia in these patients: the Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH) and Cerebral Salt Wasting Syndrome (CSWS). The two entities differ in their volume status. In SIADH, volume is expanded due to ADH-mediated renal water retention, but in CSWS, volume is diminished as a consequence of renal salt wasting, most likely attributable to an increased secretion of Brain Natriuretic Peptide (BNP) and Artrial Natriuretic Peptide (ANP). Since it is clinically difficult to distinguish between these two entities, fluid management has to be performed carefully. Salt and fluid replacement appears to be indicated in CSWS, whereas fluid restriction might be the primary approach in patients with SIADH.

[Treating hyponatraemia--not an easy task]

Chronic hyponatraemia and its therapy is a common and often underestimated problem of hospitalized patients. Usually, hyponatraemia is just one of many laboratory features found in such patients. However, rapid correction of chronic hyponatraemia can have devastating neurological consequences, i.e. osmotic myelinolysis. In the following, we describe the mechanisms leading to myelinolysis due to rapid correction of hyponatraemia and answer the questions how much, and at which rate to correct chronic hyponatremia.