Central Diabetes Insipidus
(Vasopressin-Sensitive Diabetes Insipidus)
(See also Overview of the Pituitary Gland.)
Central diabetes insipidus is a lack of vasopressin (antidiuretic hormone) that causes excessive production of very dilute urine (polyuria).
Central diabetes insipidus has several causes, including a brain tumor, a brain injury, brain surgery, tuberculosis, and some forms of other diseases.
The main symptoms are excessive thirst and excessive urine production.
The diagnosis is based on urine tests, blood tests, and a water deprivation test.
People with central diabetes insipidus usually are given the drugs vasopressin or desmopressin as a nasal spray.
Vasopressin is a hormone produced by the hypothalamus (a region of the brain that lies just above the pituitary) and stored in and released from the posterior lobe of the pituitary gland. Vasopressin helps regulate the amount of water in the body by signalling the kidneys to decrease the amount of urine they produce (see A Careful Balancing Act). Because a diuretic is a substance that increases urine production, vasopressin previously was referred to as antidiuretic hormone.
Central diabetes insipidus results from a deficiency of vasopressin. The deficiency may be
Other disorders that can cause central diabetes insipidus include accidental damage done during surgery on the hypothalamus or pituitary gland; a brain injury, particularly a fracture of the base of the skull; a tumor; sarcoidosis or tuberculosis; an aneurysm (a bulge in the wall of an artery) or blockage in the arteries leading to the brain; some forms of encephalitis or meningitis; and the rare disease Langerhans cell histiocytosis.
Nephrogenic diabetes insipidus is another type of diabetes insipidus in which there is an adequate amount of vasopressin, but abnormalities in the kidneys cause them not to respond to vasopressin.
Symptoms may begin gradually or suddenly at any age. Often the only symptoms are
The person urinates excessively and often wakes during the night to urinate. A person may drink huge amounts of fluid—4 to 40 quarts (3 to 30 liters) a day—to compensate for the fluid lost in urine. Ice-cold water is often the preferred drink. When compensation is not possible, dehydration can quickly follow, resulting in low blood pressure and shock. The person continues to urinate large quantities of dilute urine, and this excessive urination is particularly noticeable during the night.
Doctors suspect diabetes insipidus in people who produce large amounts of urine. They first test the urine for sugar to rule out diabetes mellitus (a more common cause of excessive urination). Blood tests show abnormal levels of many electrolytes, including a high level of sodium.
The water deprivation test is the best test to diagnose central diabetes insipidus. In a water deprivation test, urine production, blood electrolyte levels, and weight are measured regularly for a period of about 12 hours, during which the person is not allowed to drink. A doctor monitors the person's condition throughout the course of the test. At the end of the 12 hours—or sooner if the person has a decrease in blood pressure, an increase in heart rate or a loss of more than 5% of body weight—the doctor stops the test and injects vasopressin. The diagnosis of central diabetes insipidus is confirmed if, in response to vasopressin, the person's excessive urination stops, the urine becomes more concentrated, the blood pressure rises, and the heart beats more normally. The diagnosis of nephrogenic diabetes insipidus is made if, after the injection, the excessive urination continues, the urine remains dilute, and blood pressure and heart rate do not change.
Desmopressin (a longer acting form of vasopressin) may be taken as a nasal spray twice a day or sometimes as a tablet. The dose is adjusted to maintain the body's water balance and a normal urine output. Taking too much vasopressin can lead to fluid retention, swelling, and other problems. People with central diabetes insipidus who are undergoing surgery or are unconscious are generally given injections of vasopressin.
Sometimes central diabetes insipidus can be controlled with drugs that stimulate production of vasopressin, such as chlorpropamide, carbamazepine, clofibrate, and thiazide diuretics. These drugs are unlikely to relieve symptoms completely in people whose diabetes insipidus is severe.
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