Cerebral salt wasting and elevated brain natriuretic peptide levels after traumatic brain injury: 2 case reports

Historically, hyponatremia in patients with varying brain diseases was termed cerebral salt wasting. Hyponatremia secondary to CSW was reported to be a distinct entity from SIADH, with the distinguishing feature of decreased extracellular fluid volume. Brain natriuretic peptide, a peptide with natriuretic, vasorelaxant, and aldosterone-inhibiting properties, was recently implicated in aneurysmal SAH patients with CSW. Here, we describe 2 cases of CSW in TBI patients with elevated BNP levels. This phenomenon has not been previously described.

Two patients with TBI and hyponatremia were subject to analysis. Central lines were placed to assess volume status. Levels of BNP were measured at the onset of hypertonic saline infusion. Electrocardiogram and cardiac enzyme studies were performed to assess cardiac function. Serial imaging was performed to assess the extent of brain injury.

These patients with TBI had findings consistent with CSW with elevated BNP levels in the setting of normal cardiac function. In both cases, a high BNP level was observed after declining plasma Na levels despite aggressive hypertonic saline infusion. High BNP levels may be associated with CSW. Further studies are necessary to establish a causative role for BNP in TBI-induced CSW.