Inadequate production of, or resistance to the effects of, the pituitary hormone involved in controlling water balance
- Age, gender, genetics, and lifestyle as risk factors depend on the type
Diabetes insipidus is a rare condition in which the kidneys produce large volumes of dilute urine. The condition is not related to diabetes mellitus, although both conditions cause thirst and excessive passing of urine.
In diabetes insipidus, the body lacks or cannot fully respond to the hormone vasopressin. This hormone is produced by the hypothalamus, the part of the brain directly above the pituitary gland. However, vasopressin is stored in and secreted by the pituitary gland, which is why it is usually considered a pituitary hormone. The role of vasopressin is to maintain the water balance of the body by controlling urine production.
What are the types?
Diabetes insipidus occurs in two forms: the more common form, called cranial diabetes insipidus, and a form known as nephrogenic diabetes insipidus.
Cranial diabetes insipidus is due to the reduced secretion of vasopressin. Possible causes of this condition include a pituitary tumour, a tumour near the hypothalamus, surgery, radiotherapy, or head injuries. In some cases, the cause is not known.
In nephrogenic diabetes insipidus, the kidneys fail to respond to normal levels of vasopressin. In some cases, the condition is present from birth and is permanent. In these cases, it is more common in males because it is due to an inherited recessive gene carried on the X chromosome (see Gene disorders). The condition may also be due to chronic kidney failure or to kidney damage resulting from the use of drugs such as certain antibiotics or lithium, a mood-stabilizing drug. In such cases, the condition may be reversible.
What are the symptoms?
Symptoms of both forms of diabetes insipidus usually develop over days or weeks, but they may appear suddenly if the pituitary gland has been damaged. Symptoms may include:
Passing excessive amounts of urine.
Disturbed sleep due to the need to pass urine frequently.
If water lost from the body is not replaced, dehydration will occur. Severe dehydration may need immediate hospital treatment with intravenous fluids.
What might be done?
If your doctor suspects that you have diabetes insipidus, he or she may measure your urine volume over a 24-hour period. Also, urine output is measured after you have been deprived of fluids for several hours. If you have diabetes insipidus, you will continue to produce a large volume of urine. Your response to synthetic vasopressin is then measured. If vasopressin lowers your urine output, you probably have cranial diabetes insipidus; if output remains high, you probably have the nephrogenic form. If a tumour is suspected as the cause of the cranial form, you may also undergo imaging tests, such as MRI.
Cranial diabetes insipidus is most commonly treated with synthetic vasopressin (see Pituitary drugs). If there is an underlying cause, such as a pituitary tumour, this will be treated.
Nephrogenic diabetes insipidus that is inherited is usually treated with a low-sodium diet and thiazide diuretics, which paradoxically reduce urine volume. Treatment must be continued for life. Nephrogenic diabetes due to kidney damage may clear up as the kidneys recover; otherwise, drug treatment is needed. If you have diabetes insipidus, carry identification to alert others to the fact in an emergency.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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