American Medical Association Family Medical Guide - American Medical Association [602]
Diabetes Insipidus
Diabetes insipidus is a disorder in which a deficiency of arginine vasopressin (AVP; also called antidiuretic hormone, or ADH) causes the body to produce large quantities of diluted urine (urine that contains a high percentage of water). AVP, which is produced by the hypothalamus and released by the posterior (rear) lobe of the pituitary gland, regulates the process of water reabsorption in the body and prevents the body from producing too much urine. In normal urine production, the kidneys filter water and other substances from the blood, reabsorbing nearly all of the filtered water and leaving only urine to be eliminated from the body. The reabsorbed water is returned to the bloodstream to maintain normal concentrations of minerals, proteins, and other chemicals in the blood and other body fluids. However, in diabetes insipidus, the kidneys do not reabsorb the filtered water, and it is eliminated from the body in urine.
Diabetes insipidus usually results from damage to the hypothalamus or to the pituitary gland caused by a severe head injury. The condition may also result from scarring or damage caused by surgery on the hypothalamus or the pituitary gland, or as a side effect of radiation therapy on the pituitary or surrounding tissue. In rare cases, diabetes insipidus is caused by pressure on the posterior lobe of the pituitary gland from a pituitary tumor (see page 885). In a form of the disorder called nephrogenic diabetes insipidus, the condition results from an insensitivity of the kidney tubules to AVP; the levels of AVP in the bloodstream are normal, but the kidneys do not respond properly to reabsorb water.
Diabetes insipidus may develop gradually or occur suddenly. If not treated promptly, the disorder can quickly cause dehydration, which can result in very low blood pressure and shock (see page 162).
Symptoms
The main symptoms of diabetes insipidus are excessive thirst and passing large quantities of urine (as much as 20 quarts a day). The need to drink and urinate is strong and constant throughout the day and night.
Diagnosis
A diagnosis of diabetes insipidus is based on the symptoms and a physical examination. If your doctor suspects that you have diabetes insipidus, he or she will probably recommend that you have a water deprivation test, which can be performed in the doctor’s office. During the test, which takes several hours to complete, you will not drink any fluids. The doctor will measure your weight and the volume and concentration of your urine at regular intervals. If the volume of water in your urine remains high and your urine is diluted, you have a deficiency of AVP. To confirm the diagnosis, after the water deprivation test is stopped, the doctor gives you an injection of synthetic AVP (vasopressin). If your symptoms are relieved, you have diabetes insipidus.
Treatment
The first step in therapy for diabetes insipidus is to treat the underlying cause. The most effective treatment is vasopressin, taken either in nose drops or by mouth. The length of time you must take the drops or pills is determined mainly by the cause of the disorder. If diabetes insipidus was caused by a head injury, surgery, or radiation therapy, taking vasopressin may help the defective gland return to normal within a year, and your symptoms will disappear. If your symptoms don’t go away, you will probably have to take the medication for the rest of your life. If the disorder is caused by a pituitary tumor, your doctor may recommend surgery or radiation therapy to remove or destroy the tumor. If you have nephrogenic diabetes insipidus, your doctor may recommend restricting your salt intake and taking medications that stimulate production of AVP, such as chlorpropamide, carbamazepine, or thiazide diuretics, to help your kidneys reabsorb water.
Disorders of the Pancreas
The pancreas is a thin gland, about 6 to 8 inches