Diabetes insipidus (DI), alternately called arginine vasopressin deficiency (AVP-D) or arginine vasopressin resistance (AVP-R), is a condition characterized by large amounts of dilute urine and increased thirst. The amount of urine produced can be nearly 20 liters per day. Reduction of fluid has little effect on the concentration of the urine. Complications may include dehydration or seizures.
There are four types of DI, each with a different set of causes. Central DI (CDI) is due to a lack of vasopressin (antidiuretic hormone) production. This can be due to injury to the hypothalamus or pituitary gland or genetics. Nephrogenic DI (NDI) occurs when the kidneys do not respond properly to vasopressin. Dipsogenic DI is a result of excessive fluid intake due to damage to the hypothalamic thirst mechanism. It occurs more often in those with certain psychiatric disorders or on certain medications. Gestational DI occurs only during pregnancy. Diagnosis is often based on urine tests, blood tests and the fluid deprivation test. Diabetes insipidus is unrelated to diabetes mellitus and the conditions have a distinct mechanism, though both can result in the production of large amounts of urine.
Treatment involves drinking sufficient fluids to prevent dehydration. Other treatments depend on the type. In central and gestational DI, treatment is with desmopressin. Nephrogenic DI may be treated by addressing the underlying cause or by the use of a thiazide, aspirin or ibuprofen. The number of new cases of diabetes insipidus each year is 3 in 100,000. Central DI usually starts between the ages of 10 and 20 and occurs in males and females equally. Nephrogenic DI can begin at any age. The term "diabetes" is derived from the Greek word meaning siphon.
Signs and symptoms
Excessive urination and extreme thirst and increased fluid intake (especially for cold water and sometimes ice or ice water) are typical for DI. The symptoms of excessive urination and extreme thirst are similar to what is seen in untreated diabetes mellitus, with the distinction that the urine does not contain glucose. Blurred vision is a rarity. Signs of dehydration may also appear in some individuals since the body cannot conserve much (if any) of the water it takes in.
Extreme urination continues throughout the day and the night. In children, DI can interfere with appetite, eating, weight gain and growth, as well. They may present with fever, vomiting or diarrhea. Adults with untreated DI may remain healthy for decades as long as enough water is consumed to offset the urinary losses. However, there is a continuous risk of dehydration and loss of potassium that may lead to hypokalemia.
Cause
The several forms of diabetes insipidus are:
Central
Central (or Neurogenic) DI has many possible causes. According to the literature, the principal causes of central DI and their oft-cited approximate frequencies are as follows: Idiopathic – 30% Malignant or benign tumors of the brain or pituitary – 25% Cranial surgery – 20% Head trauma – 16%
Nephrogenic
Nephrogenic diabetes insipidus is due to the inability of the kidney to respond normally to vasopressin.
Dipsogenic
Dipsogenic DI or primary polydipsia results from excessive intake of fluids as opposed to deficiency of arginine vasopressin. It may be due to a defect or damage to the thirst mechanism, located in the hypothalamus, or due to mental illness. Treatment with desmopressin may lead to water intoxication.
Gestational
Gestational DI occurs only during pregnancy and the postpartum period. During pregnancy, women produce vasopressinase in the placenta, which breaks down antidiuretic hormone (ADH). Gestational DI is thought to occur with excessive production and/or impaired clearance of vasopressinase.
Most cases of gestational DI can be treated with desmopressin (DDAVP), but not vasopressin. In rare cases, however, an abnormality in the thirst mechanism causes gestational DI, and desmopressin should not be used.
Diabetes insipidus is also associated with some serious diseases of pregnancy, including pre-eclampsia, HELLP syndrome and acute fatty liver of pregnancy. These cause DI by impairing hepatic clearance of circulating vasopressinase.
Pathophysiology
Electrolyte and volume homeostasis is a complex mechanism that balances the body's requirements for blood pressure and the main electrolytes sodium and potassium. In general, electrolyte regulation precedes volume regulation. When the volume is severely depleted, however, the body will retain water at the expense of deranging electrolyte levels.