Diabetes Insipidus

Deficiency of anti-diuretic hormone (ADH) or insensitivity to its action

Aetiology

• Cranial causes
• Idiopathic
• Familial (DIDMOAD - Diabetes insipidus, diabetes mellitus, optic atrophy, deafness)
• Tumours, e.g. craniopharyngioma, glioma, metastases (breast)
• Infiltration, e.g. sarcoidosis, histiocyosis
• Sheehan's syndrome (pituitary infarction following post- or antepartum haemorrhage)
• Nephrogenic causes
• Idiopathic
• Renal tubular acidosis
• Hypokalaemia
• Hypercalcaemia
• Drugs, e.g. lithium, demeclocycline, glibenclamide

Clinical features

• Polyuria urine output (10-15L/day)
• Thirst
• Nocturia
• Polydipsia
• Dehydration

Differential diagnosis

• Primary polydipsia (excessive water drinking/ normal ADH secretion)

Investigations

• Cranial diabetes insipidus
• ADH decrease
• Water deprivation test
• High plasma osmolality
• Low urine osmolality
• Normal response to DDAVP
• Nephrogenic diabetes insipidus
• ADH increase
• Water deprivation test
• High plasma osmolality
• Low urine osmolality
• No response to DDAVP
• Inappropriate ADH
• ADH increase
• Plasma osmolality low
• Urine osmolality high

Management

• Treat underlying cause
• Synthetic vasopressin analogue
• DDAVP (Desmopressin)
• Carbamazepine
• Chlorpropamide