Fig. 1.

Four types of SIADH. Type A is characterized by unregulated secretion of vasopressin, type B by elevated basal secretion of vasopressin despite normal regulation by osmolality, type C by a ‘reset osmostat’ and type D by undetectable vasopressin levels (these patients may have a gain of function mutation of the V2-receptor). Especially for types C and D, the term syndrome of inappropriate antidiuresis may be more appropriate. According to present understanding, type C and D patients may not respond to vasopressin-receptor antagonists. The shaded area represents the normal response showing a rise in vasopressin secretion with increasing serum sodium concentrations. Adapted and reprinted from [32], Copyright 2006, with permission from Elsevier.