Diabetes Insipidus Signs And Symptoms Diagnosis Pathophysiology

Diabetes insipidus (DI) is a disease characterized by excretion of large amounts of severely diluted urine, which cannot be reduced when fluid intake is reduced. It denotes inability of the kidney to concentrate urine. DI is caused by a deficiency of antidiuretic hormone, or by an insensitivity of the kidneys to that hormone.

1 Signs and symptoms

Excessive urination and extreme thirst (expecially for cold water) are typical for DI. Symptoms of diabetes insipidus are quite similar to those of severely deranged diabetes mellitus, with the distinction that the urine is not sweet and there is no hyperglycemia (elevated blood glucose). Blurred vision is a rarity.

The 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 drunk to offset the urinary losses. However, there is a continuous risk of dehydration.

2 Diagnosis

In order to distinguish DI from other causes of excess urination, blood glucose and calcium need to be tested. Electrolytes can show substantial derangement; hypernatremia (excess sodiumSodium is the chemical element in the periodic table that has the symbol Na Natrium in Latin) and atom number 11. Sodium is a soft, waxy, silvery reactive metal belonging to the alkali metals that is abundant in natural compounds (especially halite). levels) are common in severe cases. UrinalysisA urinalysis (or "UA") is an array of tests performed on urine, usually used in medical diagnosis. The greater part of a urinalysis can be performed by using urine dipsticks, in which the test results can be read as color changes. A typical medical urinal shows low electrolyte levels, and measurement of urine osmolarity (or specific gravity) is generally low.

This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes measuring blood levels of ADH during this test is also necessary.

To distinguish between the main forms, desmopressinDesmopressin DDAVP , Stimate ) is a synthetic drug that mimics the action of antidiuretic hormone. It may be taken nasally or intravenously. Chemistry Desmopressin is a modified form of the hormal human vasopressin, which 1-desamino-8-D-arginine vasopress 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 central DI. If desmopressin reduces urine output and increases osmolarity, 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 or osmolarity.

If central DI is suspected, testing of other hormones of the pituitary, as well as magnetic resonance imagingMagnetic resonance imaging MRI is a method of creating images of the inside of opaque organs in living organisms as well as detecting the amount of bound water in geological structures. It is primarily used to visualise pathological or other physiological (MRI), is necessary to discover if a disease process (such as a prolactinomaA prolactinoma is a benign tumor ( adenoma) of the pituitary gland that produces a hormone called prolactin. It is the most common type of pituitary tumor. Symptoms of prolactinoma are caused by too much prolactin in the blood hyperprolactinemia) or by pr) is affecting pituitary function.

3 Pathophysiology

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 is the hypothalamus, which produces antidiuretic hormone (ADH or vasopressin) in the posterior lobe of the pituitary gland. In addition, it regulates the sensation of thirst as perceived by the cortex.

The main effector organ for fluid homeostasis is the kidney. In response to ADH, it concentrates urine in the distal tubule .

There are several forms of DI:

Central diabetes insipidus is due to damage to the hypothalamus of pituitary due to a tumor, stroke, neurosurgery or some rather rare causes (which include hemochromatosis, sarcoidosis and some genetic disorders). If the hypothalamus is damaged, the feeling of thirst may be completely absent.
Nephrogenic diabetes insipidus is due to kidney damage. This is rarer, but occurs as a side-effect to some medications (such as lithium citrate and amphotericin B), as well as in polycystic kidney disease (PKD) and sickle-cell anemia. In some cases, no cause is found.
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 ADH secretion and increases urine output. Desmopressin is ineffective, and can lead to fluid overload as the thirst remains.
Gestational DI only occurs during pregnancy. While all pregnant women produce vasopressinase in the placenta, which breaks down ADH, this can assume extreme forms in GDI. Most cases of gestational DI can be treated with desmopressin. In rare cases, however, an abnormality in the thirst mechanism causes gestational DI, and desmopressin should not be used.

4 Treatment

Central DI and gestational DI respond to desmopressin. In dipsogenic DI, desmopressin is not an option.

Desmopressin will be ineffective in nephrogenic DI. Instead, the diuretic hydrochlorothiazide (HCT or HCTZ) or indomethacin can improve NDI; HCT is sometimes combined with amiloride to prevent hyperkalemia. Again, the patient should be reminded only to drink fluids when thirsty, and not at other times.

5 Sources

The public domain document "Diabetes Insipidus", NIH Publication No. 01-4620, December 2000.

Endocrinology Nephrology

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