A disorder in which there is an increased, inappropriate secretion of antidiuretic hormone, the incidence of which is about 7 in 10,000. It is sort of opposite to diabetes insipidous.
This results in disorders of fluid and electrolyte balance, with the inability to dilute urine, lowered plasma sodium levels (hyponatremia) and fluid retention in the body.
The most common cause is a tumour that secretes ADH, most common of which are "oat cell" tumours in lung cancer.
Treatment is via fluid restrictions to daily insensible losses and finding and treating the underlying cause.
other causes:
CNS
Pulmonary
Neoplastic
Pharmacologic