Diabetes insipidus (DI) is a condition characterised by a deficiency in the action of antidiuretic hormone (ADH), also known as arginine vasopressin (AVP). ADH is synthesised by the magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus and stored in the posterior pituitary.

A deficiency in ADH secretion is known as cranial (central) DI, often referred to as arginine vasopressin deficiency (AVP-D), whereas insensitivity of the kidney to ADH is known as nephrogenic DI (arginine vasopressin resistance, AVP-R).

Causes of cranial DI

• idiopathic
• post head injury
• pituitary surgery
• craniopharyngiomas
• infiltrative
  • histiocytosis X
  • sarcoidosis
• DIDMOAD is the association of cranial Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness (also known as Wolfram's syndrome)

Causes of nephrogenic DI

• genetic:
  • more common form affects the vasopression (ADH) receptor
  • less common form results from a mutation in the gene that encodes the aquaporin 2 channel
• electrolytes
  • hypercalcaemia
  • hypokalaemia
• lithium
  • lithium desensitizes the kidney's ability to respond to ADH in the collecting ducts
• demeclocycline
• tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis
• haemochromatosis (some cases may also present with cranial DI)

Features

• polyuria
• polydipsia

Investigation