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When you hear the term "diabetes insipidus," you may immediately assume the condition is related to what's commonly known as "sugar" diabetes, or type 1 and type 2 diabetes mellitus. While the disorders share a name and have some common signs, in actuality 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 hormone that increases water absorption by your kidneys and decreases urine flow. This form of diabetes insipidus is often called central diabetes insipidus, or sometimes neurogenic diabetes insipidus.

Diabetes insipidus can also occur when your kidneys are unable to properly respond to the hormone — a condition referred to as nephrogenic insipidus. Still rarer forms can occur during pregnancy (gestational diabetes insipidus).

Treatment depends on which type of diabetes insipidus you have.

The two most common signs 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 2.5 liters per day if you have mild diabetes insipidus to 15 liters per 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 1.5 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

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 in order to conserve fluid when your body water is decreased, such as through perspiration.

In order to keep the volume and composition of body fluids balanced, the rate of fluid intake is largely governed by habits and thirst, and the rate of excretion 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 the 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 the bloodstream rather than excreting water into the 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 DI. The cause of central diabetes insipidus is damage to the pituitary gland or hypothalamus 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 DI. 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. In about one in four cases of nephrogenic DI, doctors never determine a cause.
• Gestational DI. 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.

Nephrogenic diabetes insipidus that is present at or shortly after birth usually has a genetic cause that permanently alters the kidneys' ability to concentrate the urine. Nephrogenic DI usually affects males, though women can pass the gene on to their children.

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

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.

  In children, the water deprivation test is performed under close medical supervision so that they don't lose more than 5 percent of their body weight 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 non-invasive 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
• Hypotension (low blood pressure)
• 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.

Treatment of diabetes insipidus depends on what form of the condition you have, so your doctor will want to determine which form of DI is present before beginning treatment. Following are the treatment options for the most common types of diabetes insipidus:

• Central DI. Because the cause of this form of diabetes insipidus is a lack of antidiuretic hormone (ADH), treatment is usually with a synthetic hormone called desmopressin. You can take desmopressin as a nasal spray, oral tablets, or by injection. The synthetic hormone will eliminate the increase in urination. For most people with central DI, desmopressin is a safe and effective treatment. If the condition is caused by an abnormality in the pituitary gland or hypothalamus (such as a tumor), however, your doctor will first treat the abnormality.

  If you have central DI, be sure to replace any fluid that you do lose; however, while you're taking desmopressin, drink fluids or water only when you're thirsty. This is because the drug prevents excess water excretion, which means your kidneys are making less urine and are less responsive to changes in body fluids.

  In mild cases of central DI, increased water intake may be all that you need. Your doctor may suggest a certain amount of water intake (usually more than 2.5 liters a day) to ensure proper hydration.

• Nephrogenic DI. This condition is the result of your kidneys not properly responding to ADH, so desmopressin is not a treatment option. Instead your doctor may prescribe a low-salt diet to help reduce the amount of urine your kidneys make. You'll also need to be sure to drink enough water to avoid dehydration.

  The drug hydrochlorothiazide, used alone or with other medications, may improve symptoms. Although hydrochlorothiazide is a diuretic (usually used to increase urine output), in some cases it can reduce urine output for people with nephrogenic DI.

  If symptoms from nephrogenic diabetes insipidus are due to medications you're taking, stopping these medicines may help; however, don't stop taking any medication without talking with your doctor first.

• Gestational DI. Treatment for most cases of gestational DI is with the synthetic hormone desmopressin. In rare cases, an abnormality in the thirst mechanism causes gestational DI. In these rare cases, doctors don't prescribe desmopressin.

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.