Diabetes insipidus

Diabetes insipidus (DI) is a condition characterised by either a deficiency of antidiuretic hormone, ADH, (cranial DI) or an insensitivity to antidiuretic hormone (nephrogenic DI).

Causes of cranial DI

• idiopathic
• post head injury
• pituitary surgery
• craniopharyngiomas
• histiocytosis X
• 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: the more common form affects the vasopression (ADH) receptor, the less common form results from a mutation in the gene that encodes the aquaporin 2 channel
• electrolytes: hypercalcaemia, hypokalaemia
• drugs: demeclocycline, lithium
• tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis

Features

• polyuria
• polydipsia

Investigation

• high plasma osmolality, low urine osmolality
• water deprivation test