What is Diabetes insipidus?

Diabetes insipidus (DI) is a rare endocrine disorder in which the kidneys are no longer able to conserve water or concentrate the urine. This, in turn, leads to excessive thirst (polydipsia), an increased intake of fluids and thus excessive urination (polyuria).

Despite the similar names and certain symptoms in common, including increased thirst and increased urination, diabetes mellitus and diabetes insipidus are not related diseases. In the case of DI, sometimes called “water diabetes,” the body is in an abnormal state of water diuresis (overproduction of diluted urine). With diabetes mellitus, sometimes called “sugar diabetes,” the body is in an abnormal state of osmotic diuresis (excess urine caused by high glucose).

A part of the brain called the hypothalamus is responsible for producing the antidiuretic hormone ADH, which is commonly referred to as vasopressin. This hormone signals the kidneys to conserve water by creating concentrated urine. If there is a lack of vasopressin, the kidneys will no longer absorb excess water, leading to diabetes insipidus. This causes the body to rapidly lose water in the form of dilute urine. This form of DI, commonly referred to as central diabetes insipidus, is often a result of damage to the hypothalamus or pituitary gland caused by surgery, infection, tumor or a head injury.

DI can also be caused by certain medications, such as lithium, and it can be inherited. About 25 percent of the time, a definitive cause cannot be found, according to the American Academy of Physicians. The prevalence of all types of DI is rare, occurring in 1 out of 25,000 people.

Central DI (also called neurogenic DI) can be either a temporary or permanent disorder, depending on the injury or underlying condition. Although all forms of diabetes insipidus are rare, central DI is the most common form of diabetes insipidus.

Diabetes insipidus can result from head trauma, brain tumors, infections like meningitis and encephalitis or vascular causes such as a stroke.

Types and differences of diabetes insipidus

Diabetes insipidus (DI) is an uncommon disease that develops when the kidneys are no longer able to conserve water or concentrate the urine. There are four types of DI:

In about a quarter of cases, a definitive cause cannot be found for diabetes insipidus. Physicians sometimes use the term idiopathic to describe conditions whose cause is unknown.

How is it diagnosed?

Because the most common cause of polyuria and polydipsia is diabetes mellitus (DM), diabetes insipidus (DI) may be overlooked by physicians. An incorrect diagnosis of DM instead of DI can not only cause needless suffering, but it can also lead to severe dehydration and, in rare cases, brain damage or possibly death. A proper diagnosis is also important when considering that DI may be an early sign of another serious underlying condition, such as a brain tumor.

To make a diagnosis of diabetes insipidus, a physician may take a medical history that includes:

• A review of conditions or illnesses that could be causing or contributing to dehydration
• A review of medications that the patient is taking
• A review of recent drinking, urinary and bowel habits

A physical examination should include taking vital signs including pulse, blood pressure (hypotension) and an evaluation of any difficulty swallowing. When more water than salt is being lost, the physician may attempt to rule out excessive diuretic use, infections and fever based on the medical history and physical examination.

A diagnosis of DI is also based on blood tests and urine tests. If DI is suspected, most physicians will recommend a water deprivation test. Because of the various reasons for developing DI, an ultrasound or MRI (magnetic resonance imaging) may be used to check for brain injury, tumors or any signs of kidney disease.

Some of the more common diagnostic tests used to screen for diabetes insipidus include:

• Measurements of antidiuretic hormone (ADH, also called vasopressin) and other substances in blood and urine before and during a water deprivation or dehydration test.
• MRI of the brain.
• A closely monitored administration of a synthetic antidiuretic hormone known as DDAVP.
• The water deprivation test. During this test the patient is not permitted to drink any water. The weight of the patient will be checked and urine and blood tests performed. Urine volume and the ability of the kidneys to concentrate urine is checked every hour. Blood concentration is measured every two hours.

However, if the DI appeared in infancy or early childhood or if it affects other members of the patient’s family, a genetic test may be ordered to determine if it is an inherited form of DI.

How is it treated?

Treatment options for diabetes insipidus (DI) vary greatly depending on the underlying cause of this rare condition. If possible, the cause of the underlying condition should be treated. Central DI may be controlled with medication, which normally includes some form of hormone replacement therapy. The hormone therapy includes administering vasopressin, usually as a nasal spray, tablets or injections under the skin.

However, vasopressin is not effective for patients with nephrogenic or primary polydipsic DI. Thiazide diuretics, anti-inflammatory medications or a sodium-restricted diet are often used for those who have nephrogenic DI. In addition, patients with nephrogenic DI caused by medications such as lithium often see a return of normal kidney function once the medication is stopped.

If the nephrogenic DI is the extremely rare hereditary form, increased fluid intake that matches the urine output and possibly the addition of medications that lower urine output may be all that is needed for treatment. Primary polydipsic DI is treated by limiting the patient’s fluid intake.

Depending on the underlying disorder or condition that led to DI, when properly diagnosed and treated, diabetes insipidus does not cause severe problems or reduce life expectancy.

Because complications from dehydration can lead to confusion and impaired mental function, patients with DI are urged to wear a medical alert bracelet or necklace so as to alert bystanders and healthcare workers in an emergency.

Medications

Lozol (Indapamide), Tegretol (Carbamazepine)

What might complicate it?

Complications include dehydration, electrolyte imbalance and vascular collapse.

Predicted outcome

The treatment of diabetes insipidus is straightforward with a good prognosis. The underlying cause of the disorder may have different outcomes.

Alternatives

Other diagnoses may be diabetes mellitus, misuse of diuretics (water pills) or self over-hydration (psychogenic diabetes insipidus). There is a group of disorders that affect the kidneys' response to normal levels of vasopressin. This is called nephrogenic diabetes insipidus.

Appropriate specialists

Endocrinologist, urologist, neurologist, internist, and infectious disease specialist.

Last updated 4 July 2015