What Is Diabetes Insipidus (DI)?

Diabetes Insipidus (DI) is a disease characterized by frequent and high urine output, frequent thirst and high fluid intake. With DI, the urine tends have a low concentration of solids and a very high water volume, making the urine very pale or clear. Diabetes Insipidus is not the same as diabetes mellitus (DM), or "sugar" diabetes. The word "diabetes" has Greek roots and refers to frequent urination. Since both diseases share the same urinary symptoms, they have similar names. There are four types of DI: pituitary, gestational, nephrogenic, and primary polydipsia. Each type has a different cause and method of treatment.

Pituitary DI

• Pituitary DI is the most common form and is linked to the hormone vasopressin. Vasopressin is produced by the posterior pituitary gland and prevents urination by signaling the kideys to increase urine concentration and reduce urine output. The usual cause of Pituitary DI is damage to the posterior pituitary gland, but it can also be an inherited disorder. Pituitary DI is often treated with desmopressin (DDAVP), a man-made form of vasopressin. Alcohol consumption suppresses vasopressin, which is why alcohol consumption often leads to frequent and high urine output. Alcohol-induced urination is not actually DI. It is a temporary condition and reverses once the alcohol clears the system.

Gestational DI

• Gestational DI occurs during pregnancy. The mechanism for Gestational DI is not well known, but it is believed that either preexisting damage to the pituitary is exacerbated by the pregnancy or the placenta destroys the vasopressin hormone before it can be used by the kidneys. Doctors may administer DDAVP to treat the disorder, but symptoms usually stop four to six weeks after delivery. It is possible for gestational DI to recur with each pregnancy.

Nephrogenic DI

• With nephrogenic DI, the pituitary produces vasopressin but the kidneys do not respond. Drug usage and kidney disease account for most cases of nephrogenic DI, but it is also possible to inherit the disorder. This form of DI does not respond to DDAVP because it relies on the kidneys to respond to the drug. Treating the underlying kidney disease and/or discontinuing drug usage may reverse the condition.

Primary Polydipsia DI

• Primary polydipsia DI is similar to pituitary DI except that, with primary polydipsia, the part of the brain that regulates thirst malfunctions, resulting in excessive fluid intake. In response, the pituitary stops producing vasopressin in order to rid the body of excess fluid. The drug DDAVP will stop patients from urinating but will not stop the thirst associated with primary polydipsia, putting patients at risk for water intoxication. As a result, there is no specific treatment for primary polydipsia. However, DDAVP can be used, in very small doses, to control symptoms like bed wetting, if administered before bedtime.

Diagnosing DI

• DI often mimics the symptoms of diabetes mellitus (DM), and many doctors may mistakenly diagnose a DI patient with DM. Once the doctor determines that the patient has DI, she will then need to determine what type, in order to apply the right treatment. One method to determine if a patient has primary polydipsia or pituitary DI is to deprive the patient of fluid and measure the amount of vasopressin in the blood. People with pituitary DI will have low levels of vasopressin regardless of fluid intake, whereas, with primary polydipsia, vasopressin levels should remain normal. A person with nephrogenic DI may have abnormally high levels of vasopressin as the brain tries to compensate for the lack of response from the kidneys.

DI Complications

• The biggest physical complication with DI is dehydration and electrolyte loss from excessive urination, especially if the patient is not able to immediately replace fluids. DI also interferes with daily activities and patients may suffer sleep disturbances or emotional distress from frequent night-time urination and bed wetting.