Normally, a hormone or chemical in the blood tells the kidneys when to hold on to water and when to release it. This is important for managing blood pressure. When the kidneys aren't able to retain water, the condition is called diabetes insipidus. This is not related to the more familiar diabetes mellitus (Type 2 diabetes).
Symptoms of Diabetes Insipidus
Symptoms of diabetes insipidus can happen at any age. Sometimes they arise gradually; other times suddenly. They include:
- A frequent need to pass urine, even at night
- Extreme thirst that causes a person to drink enormous quantities of water
- Dehydration, if a person isn't able to replace the fluids that he or she is losing through urine
- Imbalanced electrolytes. These are salts in the blood. The atoms or groups of atoms in these salts have an electrical charge (either negative or positive). The electrolytes are what your cells (especially nerve, heart and muscle) use to maintaining electrical currents to carry electrical impulses across themselves and to other cells. Examples of major electrolytes are sodium, potassium, calcium, choride and phosphate. A person with diabetes insipidus will have relatively high levels of sodium and potassium.
Causes and Risk Factors for Diabetes Insipidus
Diabetes insipidus can be caused in several ways:
- The body lacks the water-retaining hormone (vasopressin or ADH). This type is called neurogenic diabetes insipidus. It is sometimes referred to as cranial, central or pituitary diabetes insipidus. The hormone may be either totally or partially lacking.
- The kidneys have an abnormality that prevents them from responding to the water-retaining hormone. This is called nephrogenic diabetes insipidus.
While it is often impossible to know what the direct cause of insipidus was, the condition can sometimes be due to inherited abnormalities, tumors, injuries to the skull, diseases such as sarcoidosis or tuberculosis, blood vessel abnormalities such as aneurysms or infections such as encephalitis or meningitis.
Diagnosing Diabetes Insipidus
One of the simplest tests for diagnosing diabetes insipidus is a water deprivation test. This must be done under constant supervision because the patient can become seriously dehydrated. The test begins in the morning by weighing the patient, taking a blood sample to measure electrolyte levels and taking a urine sample. Voided urine is collected every hour. Measurements are taken of how concentrated the urine is.
At a certain point, after another blood test, the patient is given vasopressin and a final urine sample is collected an hour later. A diagnosis of diabetes insipidus can be made (or rejected) based on the changes in the person's blood and urine composition over the course of the test.
Treating Diabetes Insipidus
Without treatment diabetes insipidus can cause permanent kidney damage.
Treatment usually consists of hormone replacement and treatment of any underlying cause (such as surgical removal of a pituitary tumor) that can be addressed.
Non-hormone drugs may also be helpful, including:
- ADH-releasing drugs such as chlorpropamide, carbamazepine and clofibrate. These can reduce or eliminate the need for hormone replacement in some people who have a partial lack of vasopressin. These drugs are not effective, however, if a person has nephrogenic diabetes insipidus.
- Prostglandin inhibitors
Reducing the amount of salt consumed in the diet may also help.