Diabetes Insipidus

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• deficiency of ADH - Vasopressin or failure of kidneys to respond

History

• urine ouput 10-15 litre / day
• → dehydration if access to water impaired
• may be masked by cortisol deficiency

Causes

Cranial

• common after pituitary surgery
• Familial
  • DIDMOAD syndrome
• Idiopathic
• Tumours
  • craniopharyngioma
  • hypothalamic tumour
  • metastases
  • Lymphoma
  • Pituitary tumour
• Infection
  • Tuberculosis
  • Meningitis
  • Brain Abscess
• Infiltration
  • Sarcoidosis
  • Langerhan's cell histiocytosis
• Post-surgical
• Post-radiotherapy
• Vascular
  • Haemorrhage
  • Thrombosis
  • Sheehan's Syndrome
  • Aneurysm
• Trauma

Nephrogenic

• Familial
• Idiopathic
• Renal tubular acidosis
• Hypokalaemia
• Hypercalcaemia
• Drugs
  • Lithium
  • demeclocycline
  • glibenclamide

Differential

• primary polydipsia

Investigations

• plasma osmolality
  • high / upper end normal
• plasma sodium
  • high / upper end normal
• 24hr urine
  • high volume
• Water deprivation test
  • failure of concentration with water deprivation
  • restoration of concentration with vasopression or analogue implies a cranial cause

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