Definition: It is a syndrome characterized by the production of abnormally large volumes of dilute urine due to the decreased secretion or decreased action of AVP (arginine vasopressin). AVP is also commonly known as ADH i.e. Anti Diuretic Hormone. Cause: 1) Central D.I - aka pituitary D.I or neurohypophyseal D.I. 2) Nephrogenic D.I Central D.I occurs because of an inadequate release of ADH from the posterior pituitary. The usual causes are idiopathic, traumatic, iatrogenic (surgery,radiation), neoplastic, infective, granulomatous (TB,sarcoidosis) and congenital being a rarer cause. Nephrogenic D.I is due to the resistance to ADH at the level of the collecting duct cell. The most common cause of resistance is the use of drugs like lithium (bipolar disorders) and amphotericin. But it can rarely be due to a congenital cause. Pathogenesis: The antidiuretic effect of ADH is achieved by increasing the hydroosmotic permeability of cells that line the distal tubule and medullary ...