There are four types of diabetes insipidus including:

• Central or cranial diabetes insipidus, also called neurogenic diabetes insipidus
• Nephrogenic diabetes insipidus
• Dipsogenic diabetes insipidus due to malfunction of the thirst mechanism
• Gestational diabetes insipidus which occurs during pregnancy

Central or cranial diabetes insipidus

This occurs if there is a low level of vasopressin or antidiuretic hormone (ADH) in the body. The deficiency means the kidneys are not prevented from excreting large amounts of urine and instead large volumes of dilute urine are expelled, even when the body has become dehydrated. This also causes blood to lose water and become more concentrated and higher in salt. This results in dehydration and stimulation of the thirst centre in the hypothalamus of the brain which causes a person to drink more.

This is the most common type of diabetes insipidus and it is mainly caused by disease, infection or injury to the pituitary gland or the hypothalamus gland.

Causes

The causes of cranial diabetes insipidus include:

• Genetic inheritance

  The condition may be cause by an inherited mutation in the vasopressin gene, AVP-NPII which is transmitted to offspring in an autosomal fashion.

• Acquired disease may have the following causes:
  • Tumours of the pituitary gland (pituitary adenoma), craniopharyngiomas and spread of cancer to the brain (in around 20% of cases). Granuloma formation in the pituitary gland may be another cause.
  • Head injuries (in around 17%)
  • Brain surgery (in around 9%)
  • Meningitis and encephalitis may cause a small number of cases
  • Sheehan's syndrome and haemochromotosis or deposition of iron in pituitary/hypothalamic tissue
  • Blood vessel complications such as those during pregnancy where the blood supply to the hypothalamus and the pituitary gland may be compromised
  • Langerhans cell histiocytosis
• About a quarter of cases are idiopathic or without a known cause

Nephrogenic diabetes insipidus

This condition describes when the ADH level in the body is normal but the kidneys do not respond adequately to the hormone. This may occur due to kidney damage or medications such as lithium reducing the expression of water channels in the kidneys called aquaporins.

Causes

Nephrogenic diabetes insipidus may be caused by:

• Genetic inheritance

  Mutations in the genes that code for ADH receptors may be inherited and prevent these receptors from activating aquaporins in the kidneys. Inheritance is autosomal recessive in nature.

• Acquired disease may have the following causes:
  • Metabolic disorders such as high blood sugar, high blood calcium and low potassium
  • The use of medications such as demeclocycline or lithium which reduce aquaporin expression
  • Amyloidosis
  • Obstructive uropathy
  • Chronic kidney disease
  • Polycystic kidney disease

Other types of diabetes insipidus

• Dipsogenic diabetes insipidus arises due to malfunction of the thirst mechanism. Damage to the hypothalamus or pituitary gland may lead to this condition.
• Gestational diabetes insipidus that occurs pregnancy as a result of the placenta producing vasopressinase - an enzyme that breaks down vasopressin (ADH). This leads to ADH deficiency. The symptoms usually resolve after childbirth.