Diabetes Insipidus: An Introduction
Diabetes insipidus is a medical condition that occurs when the kidneys stop filtering urine normally. This results in a person urinating large volumes of fluid and always being thirsty. Diabetes insipidus is a rare disease.
Diabetes Insipidus Versus Diabetes Mellitus
Diabetes insipidus should not be confused with diabetes mellitus, which results from insulin deficiency or resistance, leading to high blood glucose.
Diabetes insipidus and diabetes mellitus are unrelated, although they can have similar signs and symptoms, like excessive thirst and excessive urination.
Diabetes mellitus (DM) is far more common than diabetes insipidus and receives more news coverage. DM has two forms, referred to as
type 1 diabetes (formerly called juvenile diabetes, or insulin-dependent diabetes mellitus, or IDDM) and
type 2 diabetes (formerly called adult-onset diabetes, or noninsulin-dependent diabetes mellitus, or NIDDM). Diabetes insipidus is a different form of illness altogether.
Diabetes Insipidus: Understanding Fluid Regulation
Your body has a complex system for balancing the volume and composition of body fluids. Your kidneys remove extra body fluids from your bloodstream. This fluid waste is stored in the bladder as urine. If your fluid regulation system is working properly, your kidneys make less urine to conserve fluid when the body is losing water. Your kidneys also make less urine at night when the body's metabolic processes are slower.
In order to keep the volume and composition of body fluids balanced, the rate of fluid intake is governed by thirst, and the rate of excretion is governed by the production of antidiuretic hormone (ADH), also called vasopressin. This hormone is made in the hypothalamus, a small gland located in the base of the brain. ADH is stored in the nearby pituitary gland and released from it into the bloodstream when necessary. When ADH reaches the kidneys, it directs the kidneys to concentrate the urine by returning excess water to the bloodstream and, therefore, make less urine.
Types of Diabetes Insipidus
Diabetes insipidus occurs when the precise system for regulating the kidneys' handling of fluids is disrupted.
Different types of diabetes insipidus include:
Central Diabetes Insipidus
The most common form of clinically serious diabetes insipidus, central diabetes insipidus, results from damage to the pituitary gland, which disrupts the normal storage and release of ADH.
Damage to the pituitary gland can be caused by different diseases as well as by head injuries, neurosurgery, or genetic disorders.
Nephrogenic Diabetes Insipidus
Another form,
nephrogenic diabetes insipidus, results when the kidneys are unable to respond to ADH. In nephrogenic
diabetes insipidus, the kidneys' ability to respond to ADH can be impaired by drugs (like
lithium, for example) and by chronic disorders, including:
Sometimes, the cause of nephrogenic diabetes insipidus is never discovered.
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 ADH secretion and increases urine output. This is a more rare form of diabetes insipidus.
Gestational Diabetes Insipidus
A fourth type of diabetes insipidus occurs only during pregnancy.
Gestational diabetes insipidus, which is also rare, occurs when an enzyme made by the placenta destroys ADH in the mother. The placenta is the system of blood vessels and other tissue that develops with the fetus. The placenta allows the exchange of nutrients and waste products between the mother and the fetus.
Symptoms of Diabetes Insipidus
Diabetes insipidus causes frequent urination. The large volume of urine is diluted, mostly water. To make up for lost water, you may feel the need to drink large amounts. 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.
Diagnosing Diabetes Insipidus
Because
diabetes mellitus is more common and because diabetes mellitus and diabetes insipidus have similar symptoms, a healthcare provider may suspect that a patient with diabetes insipidus has diabetes mellitus. But testing should make the diagnosis clear.
A diabetes insipidus diagnosis is based on a series of tests, including urinalysis and a fluid deprivation test.
Urinalysis
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 measuring how many particles are in a kilogram of water (osmolality) or by comparing the weight of the urine to an equal volume of distilled water (specific gravity).
Fluid Deprivation Test
A fluid deprivation test helps determine whether diabetes insipidus 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.
In some patients with possible
diabetes insipidus symptoms, an MRI (magnetic resonance imaging) scan of the brain may be necessary as well.
Treatment for Diabetes Insipidus
Treatment for Central Diabetes Insipidus
To treat the ADH deficiency that results from any kind of damage to the hypothalamus or pituitary, a synthetic hormone called desmopressin can be taken by an injection, a nasal spray, or a pill.
While taking desmopressin for
central diabetes insipidus, 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.
Treatment for Nephrogenic Diabetes Insipidus
Treatment for Dipsogenic Diabetes Insipidus
Desmopressin or other drugs should not be used to treat dipsogenic
diabetes insipidus because it 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.
Treatment for Gestational Diabetes Insipidus
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.
Diabetes Insipidus: Summary
The following points are important to keep in mind regarding diabetes insipidus:
- Diabetes insipidus is a rare condition caused by the kidneys' inability to filter urine.
- Common diabetes insipidus symptoms include excessive urination and increased thirst.
- Types of diabetes insipidus include central, nephrogenic, dipsogenic, and gestational.
- A diabetes insipidus diagnosis is based on a series of tests, including urinalysis and a fluid deprivation test.
- Diabetes insipidus treatment options depend on the type of diabetes insipidus with which a person is diagnosed.
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