Diabetes Insipidus

What Is Diabetes Insipidus?

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. These two conditions 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 non-insulin-dependent diabetes mellitus, or NIDDM). Diabetes insipidus is a different form of illness altogether.

 

Understanding Fluid Regulation in the Body

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 (see Causes of Diabetes Insipidus).

 

The different types include:

 

 

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.

This form results when the kidneys are unable to respond to ADH. The kidneys' ability to respond can be impaired by drugs (like lithium, for example) and by chronic disorders, including:

 

Sometimes, however, the cause of nephrogenic diabetes insipidus is never discovered.

 

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.

 

A fourth type 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 and 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.

 

Children with diabetes insipidus may be irritable or listless and may experience fever, vomiting, or diarrhea.

 

How Is It Diagnosed?

Because diabetes mellitus is more common and because diabetes mellitus and diabetes insipidus have similar symptoms, a healthcare provider may suspect that a person with diabetes insipidus has diabetes mellitus. However, testing should make the diagnosis clear. These tests include 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 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).

 

A fluid deprivation test helps determine whether diabetes insipidus is caused by:

 

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 people with possible diabetes insipidus symptoms, an MRI (magnetic resonance imaging) scan of the brain may be necessary as well.

 

Treatment for Diabetes Insipidus

A specialist should determine which form of diabetes insipidus is present before starting any treatment plan.

 

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.

Desmopressin will not work for this type of diabetes insipidus. Instead, you may be given a drug called hydrochlorothiazide (also called HCTZ) or indomethacin. HCTZ is sometimes combined with another drug called amiloride. This combination is sold under the brand name Moduretic^®. Again, with this combination of drugs, you should drink fluids only when you are thirsty and not at other times.

 

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.

 

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

 

Final Thoughts

The following points are important to keep in mind regarding diabetes insipidus: