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Diabetes insipidus (DI) is an uncommon disease that develops when the kidneys are no longer able to conserve water or concentrate the urine. There are four types of DI:

• Neurogenic or central DI. This form of the disease is by far the most common. It develops from a lack of antidiuretic hormone (ADH), more commonly referred to as vasopressin. Central DI is most commonly caused by brain tumors, head trauma, granulomatous (tumor-like) diseases or an autoimmune reaction, or is sometimes inherited from a parent.
  
  
• Nephrogenic DI. This form of diabetes insipidus comes from kidney defects that make the organ unable to respond to ADH. DI can develop because of hypokalemia (low potassium in the blood), hypercalcemia (excess calcium in the blood), or certain medications, such as lithium (used to treat bipolar disorders). Nephrogenic DI may be caused by various kidney disorders, such as polycystic kidney disease. It can also be inherited.

For those who have the inherited form of diabetes insipidus, symptoms can start within weeks of birth. However, they often go undetected or their significance can be missed for months and possibly even years. Early symptoms include fever, irritability, constipation, failure to thrive, lack of appetite, vomiting and high levels of sodium in the blood.

• Primary polydipsic DI. Also known as primary polydipsia or dipsogenic DI, caused by excessive fluid intake, which suppresses ADH. Frequently, polydipsic DI is seen in people with abnormally high thirst (polydipsia) as a result of psychological or emotional disturbances. These conditions can sometimes be referred to as psychogenic DI, whereas high fluid intake from fad diets is referred to as iatrogenic DI. The term “iatrogenic” generally refers to a condition caused by treatment.
  
  
• Gestagenic DI. This extremely rare form of the disease appears only during pregnancy. Gestagenic DI develops on the rare occasion that the placenta retards the production of vasopressin. It usually disappears after pregnancy, but may reoccur with subsequent pregnancies.

In about a quarter of cases, a definitive cause cannot be found for diabetes insipidus. Physicians sometimes use the term idiopathic to describe conditions whose cause is unknown.