SIADH and other hyponatremic disorders: diagnosis and therapeutic problems.

Hyponatremia is more frequently observed in elderly patients associated with exaggerated response of ADH release and attenuated response of renin-aldosterone system. Differentiation of SIADH and hyponatremia other than SIADH is essential in anticipating the therapeutic effect of water restriction to correct hyponatremia. Serum concentration of uric acid and urinary excretion of kallikrein are significant parameters in biochemical discrimination index to differentiate these two types of hyponatremia. In addition to sodium replacement, water restriction and mineral corticoid, newly developed non-peptide ADH V2 receptor antagonist, OPC-31260, seems to be a useful tool to correct hyponatremia.