The syndrome of inappropriate secretion of antidiuretic hormone

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) has been examined and reviewed. Typically, it is characterized by hyponatreinia without dehydration, urinary sodium loss and hypertonicity of the urine. Atypically, urinary sodium loss may be absent and urinary tonicity may be below that of serum; the only requirement is that the urine be less than maximally dilute. The syndrome is found with various tumors, notably oat cell carcinoma of the bronchus, which probably produce antidiuretic substance directly, and in a wide variety of disorders affecting the central nervous system or the lungs, in which there is probably abnormal release of endogenous antidiuretic hormone. The syndrome is also seen occasionally in patients with adrenal, thyroid or pituitary insufficiency. The possible role of the inappropriate release of antidiuretic hormone in all these disorders and in the hyponatremia which can occur postoperatively or in congestive heart failure or cirrhosis, requires further definition by new, specific assay technics.