NPPB and Hyponatremia: Overall, the data show that SIADH is the most common cause of hyponatremia following SAH, with acute glucocorticoid insufficiency also playing significant role Although CSWS has been reported following SAH [2,4,6], the largest prospective study to date did not find any cases, despite robust methodology and sequential measurement of both AVP and BNP [6], and CSWS seems to be very rare following SAH.