Diseases & Conditions

Diabetes insipidus

When you hear the term "diabetes insipidus," you may assume it's related to what's commonly known as "sugar" diabetes, or diabetes mellitus. While the disorders share a name and have some common signs, in fact diabetes mellitus (type 1 and type 2) and diabetes insipidus are unrelated.

Diabetes insipidus (DI) is a disorder characterized by intense thirst and by the excretion of large amounts of urine (polyuria). In most cases, it's the result of your body not properly producing, storing or releasing a key hormone, but diabetes insipidus can also occur when your kidneys are unable to properly respond to that hormone. Rarely, diabetes insipidus can occur during pregnancy (gestational diabetes insipidus).

Effective treatments are available to relieve your thirst and normalize your urine output.

The most common signs and symptoms of diabetes insipidus are:

• Extreme thirst
• Excretion of an excessive volume of diluted urine

Depending on the severity of the condition, urine output can range from 2.6 quarts (about 2.5 liters) a day if you have mild diabetes insipidus to 16 quarts (about 15 liters) a day if the condition is severe and if you're taking in a lot of fluids. In comparison, the average urine output for a healthy adult is in the range of 1.6 to 2.6 quarts (about 1.5 to 2.5 liters) a day.

Other signs may include needing to get up at night to urinate (nocturia) and bed-wetting.

Infants and young children who have diabetes insipidus may have the following signs and symptoms:

• Unexplained fussiness or inconsolable crying
• Unusually wet diapers
• Fever, vomiting or diarrhea
• Dry skin with cool extremities
• Delayed growth
• Weight loss

When to see a doctor
See your doctor immediately if you notice the two most common signs of diabetes insipidus: excessive urination and extreme thirst.

Normally, your kidneys remove excess body fluids from your bloodstream. This fluid waste is stored in your bladder as urine. When your fluid regulation system is working properly, your kidneys make less urine when your body water is decreased, such as through perspiration, in order to conserve fluid.

The volume and composition of your body fluids remain balanced through a combination of oral intake and excretion in the kidneys. The rate of fluid intake is largely governed by thirst, although your habits can increase your intake far above the amount necessary. The rate of fluid excreted by your kidneys is greatly influenced by the production of anti-diuretic hormone (ADH), also called vasopressin.

Your body makes ADH in the hypothalamus and stores the hormone in your pituitary gland, a small gland located in the base of your brain. ADH is released into your bloodstream when necessary. ADH then concentrates the urine by triggering the kidney tubules to reabsorb water back into your bloodstream rather than excreting water into your urine.

Diabetes insipidus occurs when this system is disrupted and your body can't regulate how it handles fluids. The way in which your system is disrupted determines which form of diabetes insipidus you have:

• Central diabetes insipidus. The cause of central diabetes insipidus is usually damage to the pituitary gland or hypothalamus, most commonly due to surgery, a tumor, illness (such as meningitis), inflammation or a head injury. In some cases the cause is unknown. This damage disrupts the normal production, storage and release of ADH.
• Nephrogenic diabetes insipidus. Nephrogenic diabetes insipidus occurs when there's a defect in the kidneys tubules — the structures in your kidneys that cause water to be excreted or reabsorbed. This defect makes your kidneys unable to properly respond to ADH. The defect may be due to an inherited (genetic) disorder or a chronic kidney disorder. Certain drugs, such as lithium and tetracycline, also can cause nephrogenic DI.
• Gestational diabetes insipidus. Gestational diabetes insipidus occurs only during pregnancy and when an enzyme made by the placenta — the system of blood vessels and other tissue that allows the exchange of nutrients and waste products between a mother and her baby — destroys ADH in the mother.

In about 30 percent of cases of diabetes insipidus, doctors never determine a cause.

Your doctor will perform a number of tests to diagnose diabetes insipidus, since the signs and symptoms can be caused by a number of conditions, such as diabetes mellitus. If the diagnosis of diabetes insipidus is made, your doctor will need to determine which type of diabetes insipidus you have, because the treatment is different for each form of the disease.

Some of the tests that doctors commonly use to determine the type of diabetes insipidus and in some cases, its cause, include:

• Water deprivation test. This test helps determine the cause of diabetes insipidus. You'll be asked to stop drinking fluids two to three hours before the test so that your doctor can measure changes in your body weight, urine output and urine composition when fluids are withheld. In some cases your doctor may also measure blood levels of ADH during this test.

  The water deprivation test is performed under close supervision in children and in pregnant women to make sure no more than 5 percent of body weight is lost during the test.

• Urinalysis. Urinalysis is the physical and chemical examination of urine. If your urine is less concentrated (meaning the amount of water excreted is high and the salt and waste concentrations are low), it could be due to diabetes insipidus.
• Magnetic resonance imaging (MRI) scan. An MRI of the head is a noninvasive procedure that uses powerful magnets and radio waves to construct detailed pictures of brain tissues. Your doctor may want to perform an MRI to look for abnormalities in or near the pituitary gland.

Family history
If your doctor suspects an inherited form of diabetes insipidus, he or she will look at your family history of polyuria and may suggest genetic screening.

Diabetes insipidus can cause your body to retain an inadequate amount of water to function properly, and you can become dehydrated. Dehydration can cause:

• Dry mouth
• Muscle weakness
• Low blood pressure (hypotension)
• Hypernatremia
• Sunken appearance to your eyes
• Fever or headache, or both
• Rapid heart rate
• Weight loss

Diabetes insipidus can also cause an electrolyte imbalance. Electrolytes are minerals in your blood — such as sodium, potassium and calcium — that maintain the balance of fluids in your body. Electrolyte imbalance can cause symptoms, such as headache, fatigue, irritability and muscle pains.

If you have diabetes insipidus, it's important to prevent dehydration. Your doctor will suggest how much fluid you may need to take in to avoid becoming dehydrated. Be sure to carry water with you wherever you go, in case you're in a situation where water or fluids aren't readily available.

Wear a medical alert bracelet or carry a medical alert card in your wallet so that if you have a medical emergency, a health care professional will recognize immediately your need for special treatment.