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Diabetes insipidus (DI) is a rare endocrine disorder in which the kidneys are no longer able to conserve water or concentrate the urine. This, in turn, leads to excessive thirst (polydipsia), an increased intake of fluids and thus excessive urination (polyuria).

Despite the similar names and certain symptoms in common, including increased thirst and increased urination, diabetes mellitus and diabetes insipidus are not related diseases. In the case of DI, sometimes called “water diabetes,” the body is in an abnormal state of water diuresis (overproduction of diluted urine). With diabetes mellitus, sometimes called “sugar diabetes,” the body is in an abnormal state of osmotic diuresis (excess urine caused by high glucose).

A part of the brain called the hypothalamus is responsible for producing the antidiuretic hormone ADH, which is commonly referred to as vasopressin. This hormone signals the kidneys to conserve water by creating concentrated urine. If there is a lack of vasopressin, the kidneys will no longer absorb excess water, leading to diabetes insipidus. This causes the body to rapidly lose water in the form of dilute urine. This form of DI, commonly referred to as central diabetes insipidus, is often a result of damage to the hypothalamus or pituitary gland caused by surgery, infection, tumor or a head injury.

DI can also be caused by certain medications, such as lithium, and it can be inherited. About 25 percent of the time, a definitive cause cannot be found, according to the American Academy of Physicians. The prevalence of all types of DI is rare, occurring in 1 out of 25,000 people.

Central DI (also called neurogenic DI) can be either a temporary or permanent disorder, depending on the injury or underlying condition. Although all forms of DI are rare, central DI is the most common form of diabetes insipidus.