Diabetes Insipidus

Diabetes Insipidus (DI) is a phenomenal condition in which the kidneys are unable to retain water due to anti-diuretic hormone deficiency (hyposecretion of ADH).  This results in the excretion of large amounts of dilute urine, which, in turn, makes you feel dry and excessively thirsty. Less commonly, DI may arise when the kidneys are insensitive to ADH because of receptor insensitivity to vasopressin and its analogues. Diabetes Insipidus is not related to diabetes mellitus; however, it may present with similar signs and symptoms. In the kidneys, the blood undergoes filtration and dialysis to separate blood wastes from the rest of components.

ADH is a hormone that regulates kidney function, it is secreted in the hypothalamus, which is the largest gland in the body. After its secretion ADH is then deposited in the hypophysis, which is a tiny pea-sized endocrine gland located at the base of the cerebrum. Antidiuretic hormone is released from the posterior pituitary gland to control water balance and blood pressure. It stimulates the kidneys to retain water by concentrating the urine and reducing urine volume by stimulating insertion of aquaporins or water channels into the membranes of kidney tubules, thus raising blood volume and decreasing serum osmolality.

Types

Focal Diabetes Insipidus is a type of  Diabetes insipidus (DI) that develops in the absence of ADH.

Central Diabetes Insipidus (neurogenic diabetes insipidus) is a type of  Diabetes insipidus (DI) associated with hypothalamic B-cell lymphoma (a brain Neoplasm) and Pituitary Lymphoma, It is characterized by polyuria (excessive urination volume or abnormally high urine output), which is associated with ADH deficiency (antidiuretic hormone deficiency) due to posterior pituitary impairment.

Nephrogenic Diabetes Insipidus is a type of  Diabetes insipidus (DI) that occurs when the kidneys fail to respond to ADH because of receptor insensitivity to vasopressin and its analogues.

Pathogenesis

Focal DI is mainly caused by a pathology affecting the hypothalamus or pituitary gland, it may be caused by all of the following reasons:

• A head injury (head trauma)
• Low Cerebral Perfusion Pressure and poor tissue perfusion of the affected organ. Cerebral Perfusion Pressure should be maintained above 70-80mmHg
• After a Surgery
• Hypothalamic or pituitary tumors

In some cases it was found that focal DI may run in families as x-linked recessive genetic disorder.

Unlike other forms of Diabetes insipidus (focal/central/neurogenic), Nephrogenic DI (NDI) is a form of  Diabetes insipidus (DI) that may be inherited by vertical means as x-linked recessive genetic disorder or acquired as a result of drug use (lithium therapy, treatment with amphotericin B, etc.), kidney disease (obstruction of the ureter, etc.), or metabolic disease such as hypokalemia or hypercalcemia, etc.

Nearly 90% of patients with hereditary NDI are males who have mutations in the AVPR2 gene.

NDI is mainly caused by a renal pathology affecting the nephron filtering apparatus responsible for blood filtration and reabsorption of fluid and solutes. Less commonly, Nephrogenic DI (NDI) can be inherited by vertical means as an autosomal recessive or dominant disorder.

Nephrogenic DI is less common than focal DI. However, Affected individuals suffer of polydipsia and polyuria, whereas, in most cases of hereditary NDI, affected males present soon after birth with polydipsia and polyuria. If left untreated, patients can quickly become dehydrated if they do not drink enough liquids, whereas, infants with NDS may experience repeated episodes of dehydration following low water intake, concurrent illness or if they live in a hot environment (heat exposure).

Causes of Nephrogenic DI

1- Certain medications prescribed for various medical conditions may cause NDI such as lithium, amphotericin B, demeclocycline, etc.
2- High blood calcium (hypercalcemia)
3- Kidney disorders such as polycystic kidney disease, etc.

 

 

Verified by: Dr.Diab (July 27, 2017)

Citation: Dr.Diab. (July 27, 2017). Diabetes Insipidus Definition Types and Pathogenesis. Medcoi Journal of Medicine, 14(2). urn:medcoi:article2984.