Diabetes insipidus is a form of diabetes entirely different from diabetes mellitus, though both disorders can lead to excessive urination. Diabetes mellitus is caused by impairment of the kidneys' ability to absorb water, which means that large quantities of dilute urine are produced.
Symptoms
The main symptoms of diabetes insipidus, according to the Mayo Clinic, is excessive urine output. Normally people excrete between 1.5 and 2.5 liters per day, whereas patients with diabetes insipidus can lose up to 15 liters of fluid per day to urination. As a result of this excessive urination, patients are often constantly thirsty.
Complications
One danger of diabetes insipidus is that unless the fluid that is lost through urination is replaced, the patient will become dehydrated. Dehydration can cause muscle weakness, a rapid heart rate, low blood pressure and a headache. Patients may also develop a sunken appearance in their eyes and can develop electrolyte abnormalities.
Causes
There are two main types of diabetes insipidus, according to the Clinical Center at the National Institutes of Health. Central diabetes insipidus is the most common form and is caused by a problem with the posterior pituitary gland. The posterior pituitary makes a hormone called vasopressin, which works to make the kidneys reabsorb water, which helps lower urine output. Nephrogenic diabetes insipidus is caused by the kidneys not being able to respond properly to vasopressin. In some cases, the Clinical Center explains, nephrogenic diabetes insipidus can be inherited.
Testing and Diagnosis
A diagnosis of diabetes insipidus typically involves a urinalysis and a fluid deprivation test, the National Institute of Diabetes and Digestive and Kidney Disorders explains. With urinalysis, a physician will do a thorough chemical analysis of the patient's urine to determine the levels of various substances normally dissolved in the urine. With a fluid deprivation test, the patient is not allowed to consume fluids for two to three hours in order to measure the effects of limited fluid intake on the patient's weight as well as urine composition and output. Often the patient's vasopressin levels will be measured as well.
Treatment
The treatment for patients with central diabetes insipidus usually hinges on giving them synthetic vasopressin to supplement that produced by the pituitary. Nephrogenic diabetes insipidus can be more difficult to treat, the Mayo Clinic explains. Patients may need to adopt a low-salt diet to lower their urine output. Some patients benefit from the medication hydrochlorothiazide as well.
