Understanding Diabetes Insipidus

• Diabetes Insipidus (DI) is a disorder characterized by frequent and high urine output, high fluid intake and frequent thirst. Diabetes Insipidus is not related to diabetes mellitis and often the terms "water" (for insipidus) and "sugar" (for mellitus) are used to differentiate the two. The word "diabetes" has Greek roots and refers to frequent urination. Both disorders share the same urinary symptoms, hence the 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 caused by a lack of vasopressin. Vasopressin is a hormone, produced by the posterior pituitary, that increases the concentration of the urine and reduces urine output. Pituitary DI usually results from damage or injury to the posterior pituitary gland, but it may also be an inherited disorder. Some forms of pituitary DI have no clear cause, the pituitary simply does not produce enough vasopressin. This form of DI is often treated with desmopressin (DDAVP), a modified form of vasopressin. Interestingly, alcohol suppresses the production of vasopressin, which is why alcohol consumption often leads to frequent and high urine output. However, alcohol-induced urination is not DI, is temporary and reverses once the alcohol clears the system.
  
  

Gestational DI

• Gestational DI occurs during pregnancy and may be caused by damage to the pituitary or if the placenta destroys the vasopressin hormone before it can be used by the kidneys. In some instances, DDAVP is used to treat the disorder but the condition usually stops four to six weeks after delivery. However, it is possible for gestational DI to recur with each pregnancy.
  
  

Nephrogenic DI

• With nephrogenic DI, the pituitary produces vasopressin but the kidneys fail to respond. Drugs and kidney disease are two causes of nephrogenic DI, but the disorder can also be inherited. This form of DI does not respond to DDAVP but treating the kidney disease or discontinuing the drug may reverse the condition.
  
  

Primary Polydipsia DI

• Primary Polydipsia DI is similar to pituitary DI in that vasopressin is also a factor. However, with primary DI, the part of the brain that regulates thirst malfunctions resulting in excessive fluid intake. The excessive fluid intake suppresses vasopressin production.
  Doctors differentiate between primary polydipsia and pituitary DI by applying stimulus like fluid deprivation and measuring the amount of vasopressin in the blood. DDAVP stops the excessive urination but does not stop the excessive thirst. As a result, people with primary polydipsia DI taking DDAVP are at risk for water intoxication. Due to this risk, there is no specific treatment for primary polydipsia DI but symptoms, like bed wetting, can be controlled with small doses of DDAVP taken before bed.
  There is a subset of primary DI called psychogenic polydipsia---a psychosomatic disorder with no present treatment.