Diabetes Insipidus: Types And Diagnosis

Diabetes Insipidus: Types And Diagnosis

Diabetes insipidus is characterized by excretion of large amounts of dilute urine, which disrupts your body's water regulation. To make up for lost water, you may feel the need to drink large amounts of water. You are likely to urinate frequently, even at night, which can disrupt sleep or, on occasion, cause bedwetting. Because of the excretion of abnormally large volumes of dilute urine, you may quickly become dehydrated if you do not drink enough water. Children with Diabetes Insipidus may be irritable or listless and, in some cases, may have fever, vomiting, or diarrhea.

Central Diabetes Insipidus

Damage to the pituitary gland can be caused by different diseases as well as by head injuries, neurosurgery, or genetic disorders. To treat the resulting antidiuretic hormone deficiency, a synthetic hormone called desmopressin can be taken by an injection, a nasal spray, or a pill. While taking desmopressin, you should drink fluids or water only when you are thirsty and not at other times. This is because the drug prevents water excretion and water can build up now that your kidneys are making less urine and are less responsive to changes in body fluids.

Nephrogenic Diabetes Insipidus

The kidneys' ability to respond to antidiuretic hormone can be impaired by drugs (like lithium, for example) and by chronic disorders including polycystic kidney disease, sickle cell disease, kidney failure, partial blockage of the ureters, and inherited genetic disorders. Sometimes the cause of nephrogenic Diabetes Insipidus is never discovered.

Desmopressin will not work for this form of Diabetes Insipidus. Instead, you may be given a drug called hydrochlorothiazide (also called HCTZ) or indomethacin. HCTZ is sometimes combined with amiloride. Again, you should drink fluids only when you are thirsty and not at other times.

Dipsogenic Diabetes Insipidus

A third type of Diabetes Insipidus is caused by a defect in 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  Antidiuretic hormone secretion and increases urine output. Desmopressin or other drugs should not be used to treat dipsogenic Diabetes Insipidus because they may decrease urine output but not thirst and fluid intake. This fluid "overload" can lead to water intoxication, a condition that lowers the concentration of sodium in the blood and can seriously damage the brain.

Gestational Diabetes Insipidus

A fourth type of Diabetes Insipidus occurs only during pregnancy. Gestational Diabetes Insipidus occurs when an enzyme made by the placenta destroys antidiuretic hormone in the mother. The placenta is the system of blood vessels and other tissue that develops with the fetus. The placenta allows exchange of nutrients and waste products between mother and fetus.

Most cases of gestational Diabetes Insipidus can be treated with desmopressin. In rare cases, however, an abnormality in the thirst mechanism causes gestational Diabetes Insipidus, and desmopressin should not be used.

A specialist should determine which form of Diabetes Insipidus is present before starting any treatment.

Diagnosis of Diabetes Insipidus

Because Diabetes mellitus is more common and because Diabetes mellitus and Diabetes Insipidus have similar symptoms, a health care provider may suspect that a patient with Diabetes Insipidus has Diabetes mellitus. But testing should make the diagnosis clear.

Your physician must determine which type of Diabetes Insipidus is involved before proper treatment can begin. Diagnosis is based on a series of tests, including urinalysis and a fluid deprivation test.

Urinalysis is the physical and chemical examination of urine. The urine of a person with Diabetes Insipidus will be less concentrated. Therefore, the salt and waste concentrations are low, and the amount of water excreted is high. A physician evaluates the concentration of urine by testing its specific gravity or osmolality.

A fluid deprivation test helps determine whether Diabetes Insipidus is caused by (1) excessive intake of fluid, (2) a defect in antidiuretic hormone production, or (3) a defect in the kidneys' response to antidiuretic hormone. This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes measuring blood levels of antidiuretic hormone during this test is also necessary.

In some patients, an MRI (magnetic resonance imaging) of the brain may be necessary as well.

Diabetes Insipidus versus Diabetes Mellitus

Diabetes Insipidus should not be confused with diabetes mellitus, which results from insulin deficiency or resistance. Diabetes insipidus and diabetes mellitus are unrelated, although they can have similar signs and symptoms, like excessive thirst and excessive urination.

Diabetes mellitus is far more common than Diabetes Insipidus and receives more news coverage. Diabetes mellitus has two forms, referred to as type 1 diabetes (formerly called juvenile diabetes, or insulin-dependent diabetes mellitus) and type 2 diabetes (formerly called adult-onset diabetes, or noninsulin-dependent diabetes mellitus). Diabetes Insipidus is a different form of illness altogether.