Description, Causes and Risk Factors:
Chronic excretion of very large amounts of pale urine of low specific gravity, causing dehydration and extreme thirst; ordinarily results from inadequate output of pituitary antidiuretic hormone; the urine abnormalities may be mimicked as a result of excessive fluid intake, as in psychogenic polydipsia.
Diabetes insipidus is a rare disorder of water metabolism. This means that the balance between how much water or fluid you drink is not balanced with the fluid you urinate. Diabetes insipidus is caused by a lack of, or nonresponse to, the antidiuretic hormone vasopressin. This hormone controls water balance by concentrating urine. Patients with diabetes insipidus urinate too much, so they need to drink a lot to replace the fluid they lose.
Vasopressin is made by the cells of the hypothalamus (located in the brain) and is stored and secreted by another part of the brain called the posterior pituitary gland. The antidiuretic hormone is then released into the bloodstream where it causes tubules within the kidney to reabsorb water. Water that cannot be reabsorbed is passed out of the body in the form of urine. Decreased secretion of vasopressin causes less water to be reabsorbed and more urine to be formed. When vasopressin is present at normal levels, more water is reabsorbed and less urine is formed.
Diabetes insipidus is usually caused by a change or abnormality in either the pituitary gland, the stalk connecting the pituitary to the brain, or within the hypothalamus itself. These changes can be due to the presence of a cyst or tumour (e.g. craniopharyngioma or germinoma) or by the in?ltration with a chronic in?ammation. The symptoms of excess thirst and urine excretion may be the ?rst signs that there is something wrong. Diabetes insipidus may occur on its own, or together with other pituitary hormone de?ciencies (multiple pituitary hormone de?ciency or MPHD).
Diabetes insipidus may occur without an identi?ed cause. This is called idiopathic diabetes insipidus. It is very important that an endocrinologist carefully checks all people with diabetes insipidus on several occasions, over months or years. This is to ensure that a small tumour does not cause the problem, which may have not been visible when the person was ?rst investigated. This is particularly important in children with a diagnosis of `idiopathic' diabetes insipidus.
Very rarely, diabetes insipidus is passed from the parents to the child (hereditary). In some cases it may affect the newborn baby who will have problems with dehydration but in other cases the symptoms may not appear until the child is up to one year old. This cause is very unusual.
Finally, diabetes insipidus can also result from surgery to the area in or around the pituitary gland
. This type of diabetes insipidus may be temporary, lasting only a few days and requiring little or no treatment. However, in some cases, the diabetes insipidus may be permanent.
Diabetes insipidus is uncommon in the United States, with a prevalence of 1 case per 25,000 population. No significant sex differences in central or nephrogenic diabetes insipidus exist: male and female prevalences are equal.
The prognosis is generally excellent, depending upon the underlying illness. Mortality is rare in adults as long as water is available. Severe dehydration, hypernatremia, fever, cardiovascular collapse
, and death can ensue in children, elderly people, or in those with complicating illnesses.
The presenting symptoms of DI are thus excessive urine output and excessive thirst. Depending on the degree to which ADH secretion is lost the symptoms can be quite mild or so great that some affected children virtually give up eating and lose a lot of weight. If fluid is not immediately available they will drink from flower vases, lavatory cisterns, puddles or anywhere else. In general affected children remain well but if they become dehydrated they may seem obviously ill. When these symptoms are first noticed many parents and professionals naturally assume this is a behavioral problem and try to restrict the child's drinking. This is obviously very upsetting for a child with severe thirst but is fortunately seldom harmful.
The diagnosis of diabetes insipidus can usually be made by comparing the concentration of salt and water in blood (serum osmolarity) and urine (urine osmolarity) in early morning samples. This needs to be done after an overnight fast and before the person has eaten or drunk anything. If the problem seems to be severe when the affected person is ?rst seen by a doctor, it may be dangerous to undertake an overnight fast as dehydration may occur during this time. Under these circumstances, the fast should occur in hospital during the day.
The two most common tests used to diagnose diabetes insipidus are the following:
- Water deprivation test/vasopressin test.
- Hypertonic saline infusion test.
The first step in treating this disease is correct diagnosis. In addition to the medications available, balancing your water or fluid intake with your urine output is also part of treatment. If this disorder is untreated, you could become seriously dehydrated, and your body will not have enough water to function.
In an emergency, most patients with diabetes insipidus (DI) can drink enough fluid to replace their urine losses. Replace losses with dextrose and water or an intravenous (IV) fluid that is hypoosmolar with respect to the patient's serum. Avoid hyperglycemia, volume overload, and overly rapid correction of hypernatremia. A good rule of thumb is to reduce serum sodium by 0.5 mmol/L every hour. The water deficit may be calculated on the basis of the assumption that body water is approximately 60% of body weight.
In case of inadequate thirst, desmopressin is the drug of choice. A synthetic analogue of antidiuretic hormone (ADH), desmopressin is available in subcutaneous, intranasal, and oral preparations. Generally, it can be administered 2-3 times per day. Patients may require hospitalization to establish fluid needs. Frequent electrolyte monitoring is recommended.
Alternatives to desmopressin as pharmacologic therapy for DI include synthetic vasopressin and the nonhormonal agents chlorpropamide, carbamazepine, clofibrate (no longer on the US market), thiazides, and indomethacin (limited efficacy).
In central DI, the primary problem is a hormone deficiency; therefore, physiologic replacement with desmopressin is usually effective. Use a nonhormonal drug for central DI if response is incomplete or desmopressin is too expensive. Nonhormonal drugs usually are more effective in treating nephrogenic DI.
Monitor for fluid retention and hyponatremia during initial therapy. Follow the volume of water intake and the frequency and volume of urination, and inquire about thirst. Monitor serum sodium, 24-hour urine volumes, and specific gravity. Request posthospitalization follow-up visits with the patient every 6-12 months. Patients with normal thirst mechanisms can usually self-regulate.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.