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What is diabetes insipidus?
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. 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.
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 sodium levels) are common in severe cases. Urinalysis shows low electrolyte levels, and measurement of urine osmolarity (or specific gravity) is generally low. A fluid deprivation test helps determine whether DI is caused by: excessive intake of fluid; a defect in ADH production; a defect in the kidneys' response to ADH. 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, desmopressin 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 imaging (MRI), is necessary to discover if a disease process (such as a prolactinoma) is affecting pituitary function.
There are several forms of diabetes insipidus: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.
Central diabetes insipidus and gestational diabetes insipidus respond to desmopressin. In dipsogenic diabetes insipidus, 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.
More information on diabetes mellitus
What is diabetes mellitus? - Diabetes mellitus is a a condition characterized by hyperglycemia resulting from the body's inability to use blood glucose for energy. Diabetes mellitus can result in coma. Over time, complications can include nerve injury, blindness, kidney failure, and premature atherosclerosis with all of its complications.
What causes diabetes mellitus? - Diabetes mellitus is a disorder caused by insufficient production of the hormone insulin by the pancreas, or insensitivity of cells to the effects of insulin. Insulin is responsible for the absorption of glucose into cells for their energy needs and into the liver and fat cells for storage.
What is insulin? - Insulin is a hormone that is produced by specialized cells (beta cells) of the pancreas. In addition to helping glucose enter the cells, insulin is also important in tightly regulating the level of glucose in the blood.
What types of diabetes mellitus are there? - There are four main types of diabetes mellitus. They are type 1 diabetes mellitus, type 2 diabetes mellitus, type 3, and Gestational diabetes mellitus (type 4).
What is type 1 diabetes? - Formerly known as juvenile diabetes or insulin-dependent diabetes, type 1 diabetes is a life-long condition in which the pancreas stops making insulin. Type 1 diabetes develops most often in young people but can appear in adults.
What is type 2 diabetes? - Type 2 diabetes is the most common form of diabetes mellitus. People with type 2 diabetes produce insulin, but either do not make enough insulin or their bodies do not use the insulin they make. Type 2, also known as non-insulin dependent diabetes, typically occurs after the age of 40 years.
What're signs and symptoms of diabetes mellitus? - Type 2 diabetes almost always has a slow onset (often years). Early symptoms of Type 1 diabetes are often polyuria (frequent urination) and polydipsia (increased thirst, and consequent increased fluid intake).
What is diabetes insipidus? - 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.
What is diabetic coma? - Diabetic coma is a medical emergency in which a person with diabetes is unconscious because the blood glucose level is too low or too high. Patients with diabetes mellitus type 1 are especially prone to this condition.
What are the complications of diabetes mellitus? - Many people with diabetes mellitus eventually develop complications. A very common short-term complication of diabetes mellitus is hypoglycemia (abnormally low blood sugar levels).
How to diagnose diabetes mellitus? - The diagnosis of type 1 diabetes is usually prompted by recent symptoms of excessive urination (polyuria) and excessive thirst (polydipsia), often accompanied by weight loss. The diagnosis of other types of diabetes is made in many other ways.
Diagnosis protocol for diabetes - People over age 45 should be tested for diabetes. If the first blood glucose test is normal, they should be re-tested every three years. A diagnosis of diabetes is made when any three of these tests is positive, followed by a second positive test on a different day.
What is the treatment for diabetes? - Diabetes is a chronic disease with no cure, but it can almost always be managed effectively. Nowadays, the goal for diabetics is to avoid or minimize chronic diabetic complications, as well as to avoid acute problems of hyperglycemia or hypoglycemia.
What type of diabetes diet is suggested? - For some people with diabetes mellitus, a healthy diet and weight loss is enough to keep glucose levels in the blood normal.
What medications are available for diabetes? - Oral diabetes medicines, or oral hypoglycemics, can lower blood glucose in people who have diabetes, but are able to make some insulin. Six FDA-approved oral diabetes medications are now on the market.
How to prevent diabetes? - Diabetes prevention is proven, possible, and powerful. Studies show that people at high risk for type 2 diabetes can prevent or delay the onset of the disease by losing 5 to 7 percent of their body weight.
What should a child diabetes do every day? - To control diabetes and prevent complications, blood glucose levels must be as close to a "normal" range as safely possible. Families should work with a health care provider to help set a child's or teen's targets for blood glucose levels.
Smoking and diabetes - There is a growing body of evidence to suggest that smoking is an independent risk factor for diabetes and that among people with diabetes, smoking aggravates the risk of serious disease and premature death.