Diabetes Insipidus Definition : It is a condition characterized by excessive thirst and polyurea secondary to deficiency of vasopressin (antidiuretic hormone ).excessive thirst

Signs and Symptoms 1.Polyurea Excretion of large quantity of dilute urine with increased frequency of voiding is called polyuria Daily output is 4 to 12 liters. 2.Polydypsia Intake of excess water Because of polyuria,thirst center in hypothalamus results in intake of large quantity of water

Classification of diabetes insipidus 1- Neurogenic (central type) Neurogenic diabetes insipidus, more commonly known as central diabetes insipidus, is due to a lack of vasopressin production in the brain (defect in hypothalamus,hypothalamic pituitary axis or in the posterior pituitary gland). 2- Nephrogenic Nephrogenic diabetes insipidus is due to the inability of the kidney to respond normally to vasopressin.

Classification of diabetes inspidus 3- Dipsogenic Dipsogenic DI is due to a defect or damage to the thirst mechanism, which is located in the hypothalamus.This defect results in an abnormal increase in thirst and fluid intake that suppresses vasopressin secretion and increases urine output. 4- Gestational Gestational DI is thought to occur with excessive vasopressinase production from the placenta which destroy vasopressin.

Pathophysiology Hypothalamus has role in : 1- the hypothalamus regulates the sensation of thirst by sensing increases in serum osmolarity and relaying this information to the cortex. 2-The regulation of urine production as it produces ADH which stored in the posterior lobe of the pituitary gland. ADH acts by increasing water permeability in the collecting ducts and distal convoluted tubules. The increase in permeability allows for reabsorption of water into the bloodstream, thus concentrating the urine. Regulating amount of urine output is important to maintain Electrolyte and fluid volume homeostasis inside body which determine blood pressure. The body's normal response to dehydration is to concentrate urine and conserve water, so urine becomes more concentrated and urination becomes less frequent. Those with DI continue to urinate large amounts of dilute urine in spite of not drinking any fluids.

Diagnosis To distinguish DI from other causes of excess urination: 1- blood glucose levels need to be tested to exclude diabetes mellitus. 2- Measurement of blood electrolytes can reveal a high sodium level (hypernatremia as dehydration develops) in case of DI. 3- Urinalysis demonstrates a dilute urine with a low specific gravity. 4 - A fluid deprivation test helps determine whether DI is caused by: excessive intake of fluid (primary polydypsia) a defect in ADH production a defect in the kidneys' response to ADH. To distinguish between the main forms, desmopressin(synthetic form of vasopressin) stimulation is also used; desmopressin can be taken by injection, a nasal spray, or a tablet. While taking desmopressin, a patient should drink fluids or water only when thirsty and not at other times, as this can lead to sudden fluid accumulation in the central nervous system. If desmopressin reduces urine output, the pituitary production of ADH is deficient, and the kidney responds normally. If the DI is due to renal pathology, desmopressin does not change either urine output. If central DI is suspected, testing of other hormones of the pituitary, as well as magnetic resonance imaging, is necessary to discover if a disease process (such as a prolactinoma, or histiocytosis, syphilis, tuberculosis or other tumor or granuloma) is affecting pituitary function. Most people with this form have either experienced past head trauma or have stopped ADH production for an unknown reason.

Differences between diabetes mellitus (DM)and diabetes insipidus (DI) Although both DM,DI have a common word diabetes which mean excretion of large amounts of urine (polyurea),but they are two entirely separate conditions with unrelated mechanisms. In case of diabetes insipidus: 1- the cause of polyuria is either a problem with the production of antidiuretic hormone (cranial diabetes insipidus) or kidney's response to antidiuretic hormone (nephrogenic diabetes insipidus), whereas diabetes mellitus causes polyuria via a process called osmotic diuresis, due to the high blood sugar leaking into the urine and taking excess water along with it.osmotic diuresis 2- no hyperglycemia or glucose in urine in case of diabetes insipidus.