Diabetes Insipidus
Diabetes insipidus is a rare condition characterized by severe thirst and extremely frequent urination. In most cases, the disorder results from the body's failure to produce, store, release, or respond properly to a hormone that controls fluid balance in the body. In spite of the similarity in their names diabetes insipidus is unrelated to diabetes mellitus, an autoimmune illness involving insulin deficiency.
Types of Diabetes Insipidus
Normally, the balance of fluids in the body is maintained through thirst that prompts fluid intake and excretion of fluid by the kidneys through urination. The rate of fluid excretion is determined, to a large degree, by an anti-diuretic hormone (ADH) known as vasopressin. There are several types of diabetes insipidus; in all but one, the level of ADH becomes abnormal.
Central Diabetes Insipidus
This variety of diabetes insipidus in adults usually results from damage to the pituitary gland or hypothalamus, most often from a head injury or inflammation, an illness like meningitis, surgery in the region, or a tumor. In children, central diabetes insipidus is frequently a hereditary disorder.
Nephrogenic Diabetes Insipidus
Nephrogenic diabetes insipidus results from a defect in the kidney tubules that makes the kidneys unable to respond appropriately to ADH. The defect may be of genetic origin, develop because of chronic kidney disease, or be caused by certain medications, such as lithium or one of the tetracycline antibiotics.
Gestational Diabetes Insipidus
During a small number of pregnancies, an enzyme produced by the placenta effectively destroys ADH in the mother, resulting in gestational diabetes insipidus.
Primary Polydipsia
Primary polydipsia, also referred to as psychogenic polydipsia, does not result from a problem with ADH production or processing, but is rather caused simply by an excessive intake of fluids. Primary polydipsia can be caused by abnormal thirst that results from an abnormality in the hypothalamus, dry mouth syndrome, or from a psychiatric illness.
Symptoms of Diabetes Insipidus
The most common symptoms of diabetes insipidus, in both adults and children, are extreme thirst and excessive excretion of dilute urine. Other symptoms may include:
- Nighttime urination or bedwetting
- Decreased appetite, weight loss, or lack of growth
- Vomiting or diarrhea
- Fever
- Dry skin
In infants and young children, crying and the inability to be consoled can be signs of this disorder.
Diagnosis of Diabetes Insipidus
In order to diagnose diabetes insipidus, a number of tests may be taken, including the following:
- Urinalysis
- Blood tests
- Water deprivation test
- MRI of the brain and pituitary gland
- Genetic testing
The water deprivation test is closely monitored, especially when administered to children and pregnant women, to ensure that the body weight does not decrease by more than 5 percent during testing.
Treatment of Diabetes Insipidus
The majority of cases of diabetes insipidus are not severe enough to cause complications and can usually be managed by having the patient drink enough fluid to prevent dehydration. When the condition is severe enough to require other treatment, the type of treatment varies according to the type of diabetes insipidus. When the disorder is caused by a tumor or other abnormality, the underlying condition must be directly addressed.
Central Diabetes Insipidus and Gestational Diabetes Insipidus
These types of diabetes insipidus are both caused by a lack of vasopressin, so patients are normally treated by the administration of a synthetic hormone which performs the same function, known as desmopressin.
Nephrogenic Diabetes Insipidus
Because this type of diabetes insipidus is the result of a kidney malfunction, administration of desmopressin is not a viable treatment option. Instead, patients are prescribed a low-salt diet and required to drink enough water to avoid becoming dehydrated. Oddly, a drug normally used as a diuretic (hydrochlorothiazide) is sometimes helpful in reducing urine output in patients with nephrogenic diabetes insipidus.
Primary Polydipsia
The only treatment for this type of diabetes insipidus is decreasing the patient's fluid intake. When dry mouth syndrome is a contributing factor, it must be addressed. When the condition is the result of a psychiatric problem, medication and cognitive behavioral therapy may be necessary to treat the underlying condition.
Usually, once accurately diagnosed, diabetes insipidus can be treated effectively.