Несахарный диабет: причины, симптомы и лечение.

Condition characterized by large amounts of dilute urine and increased thirst

Excessive urination and extreme thirst and increased fluid intake (especially for cold water and sometimes ice or ice water) are typical for DI. The symptoms of excessive urination and extreme thirst are similar to what is seen in untreated diabetes mellitus, with the distinction that the urine does not contain glucose. Blurred vision is a rarity. Signs of dehydration may also appear in some individuals since the body cannot properly regulate the amount of the water it takes in. Extreme urination continues throughout the day and the night. In children, DI can interfere with appetite, eating, weight gain and growth, as well. They may present with fever, vomiting or diarrhea. Adults with untreated DI may remain healthy for decades as long as enough water is consumed to offset the urinary losses. However, there is a continuous risk of dehydration and loss of potassium that may lead to hypokalemia.

Nephrogenic diabetes insipidus is due to the inability of the kidney to respond normally to vasopressin.

Dipsogenic DI or primary polydipsia results from excessive intake of fluids as opposed to deficiency of arginine vasopressin. It may be due to a defect or damage to the thirst mechanism, located in the hypothalamus, or due to mental illness. Treatment with desmopressin may lead to water intoxication.

Gestational DI occurs only during pregnancy and the postpartum period. During pregnancy, women produce vasopressinase in the placenta, which breaks down antidiuretic hormone (ADH). Gestational DI is thought to occur with excessive production and/or impaired clearance of vasopressinase. Most cases of gestational DI can be treated with desmopressin (DDAVP), but not vasopressin. In rare cases, however, an abnormality in the thirst mechanism causes gestational DI, and desmopressin should not be used. Diabetes insipidus is also associated with some serious diseases of pregnancy, including pre eclampsia, HELLP syndrome and acute fatty liver of pregnancy. These cause DI by impairing hepatic clearance of circulating vasopressinase.

Electrolyte and volume homeostasis is a complex mechanism that balances the body's requirements for blood pressure and the main electrolytes sodium and potassium. In general, electrolyte regulation precedes volume regulation. When the volume is severely depleted, however, the body will retain water at the expense of deranging electrolyte levels. The regulation of urine production occurs in the hypothalamus, which produces ADH in the supraoptic and paraventricular nuclei. After synthesis, the hormone is transported in neurosecretory granules down the axon of the hypothalamic neuron to the posterior lobe of the pituitary gland, where it is stored for later release. In addition, the hypothalamus regulates the sensation of thirst in the ventromedial nucleus by sensing increases in serum osmolarity and relaying this information to the cortex. Neurogenic/central DI results from a lack of ADH; occasionally it can present with decreased thirst as regulation of thirst and ADH production occur in close proximity in the hypothalamus. It is encountered as a result of hypoxic encephalopathy, neurosurgery, autoimmunity or cancer, or sometimes without an underlying cause (idiopathic). The main effector organ for fluid homeostasis is the kidney. ADH acts by increasing water permeability in the collecting ducts and distal convoluted tubules; specifically, it acts on proteins called aquaporins and more specifically aquaporin 2 in the following cascade. When released, ADH binds to V2 G protein coupled receptors within the distal convoluted tubules, increasing cyclic AMP, which couples with protein kinase A, stimulating translocation of the aquaporin 2 channel stored in the cytoplasm of the distal convoluted tubules and collecting ducts into the apical membrane. These transcribed channels allow water into the collecting duct cells. The increase in permeability allows for the reabsorption of water into the bloodstream, thus concentrating the urine. Nephrogenic DI results from a lack of aquaporin channels in the distal collecting duct (decreased surface expression and transcription). It is seen in lithium toxicity, hypercalcemia, hypokalemia, or the release of ureteral obstruction. Therefore, a lack of ADH prevents water reabsorption and the osmolarity of the blood increases. With increased osmolarity, the osmoreceptors in the hypothalamus detect this change and stimulate thirst. With increased thirst, the person now experiences a polydipsia and polyuria cycle. Hereditary forms of diabetes insipidus account for less than 10% of the cases of diabetes insipidus seen in clinical practice.

Treatment involves drinking sufficient fluids to prevent dehydration. Amiloride has additional benefit of blocking Na uptake. Thiazide diuretics are sometimes combined with amiloride to prevent hypokalemia caused by the thiazides. It seems paradoxical to treat an extreme diuresis with a diuretic, and the exact mechanism of action is unknown but the thiazide diuretics will decrease distal convoluted tubule reabsorption of sodium and water, thereby causing diuresis. This decreases plasma volume, thus lowering the glomerular filtration rate and enhancing the absorption of sodium and water in the proximal nephron. Less fluid reaches the distal nephron, so overall fluid conservation is obtained. Lithium induced nephrogenic DI may be effectively managed with the administration of amiloride, a potassium sparing diuretic often used in conjunction with thiazide or loop diuretics. Clinicians have been aware of lithium toxicity for many years, and traditionally have administered thiazide diuretics for lithium induced polyuria and nephrogenic diabetes insipidus. However, amiloride has recently been shown to be a successful treatment for this condition.

The word "diabetes" (,/d//aɪ//.//ə/'/b//iː//t//iː//z/ or ,/d//aɪ//.//ə/'/b//iː//t//ᵻ//s/) comes from Latin diabētēs, which in turn comes from διαβήτης, which literally means "a passer through; a siphon". Ancient Greek physician Aretaeus of Cappadocia (fl. in the first century CE) used that word, with the intended meaning "excessive discharge of urine", as the name for the disease. Ultimately, the word comes from Greek διαβαίνειν (diabainein), meaning "to pass through", which is composed of δια (dia ), meaning "through" and βαίνειν (bainein), meaning "to go". The word "diabetes" is first recorded in English, in the form "diabete", in a medical text written around 1425. "Insipidus" comes from Latin language insipidus (tasteless), from Latin: in "not" + sapidus "tasty" from sapere "have a taste"—the full meaning is "lacking flavor or zest; not tasty". Application of this name to DI arose from the fact that diabetes insipidus does not cause glycosuria (excretion of glucose into the urine). In a large survey conducted amongst patients with central diabetes insipidus, the majority were in favor of changing the disease's name to "vasopressin deficiency" to avoid confusion with diabetes mellitus.