Kidneys are unable to concentrate urine

Aetiology

Cranial (central) DI

• Occurs when there is insufficient levels of circulating ADH

Familial - very rare

• Isolated in most causes
• DIDMOAD

Acquired

• Idiopathic in 50% - often autoimmune
• Tumours - craniopharyngioma, hypothalamic tumour, metastases, pituitary (very rare)
• Trauma - road accidents, skull fracture, external irradiation
• Infiltrations - sarciodosis
• Infections - tuberculosis, meningitis, inflammatory disorders of hypothalamus and pituitary

Nephrogenic

• Characterised by renal resistance to ADH
• Causes include idiopathic, familial (AVPR2 receptor mutations) and renal disease

Clinical features

• Polydipsia
• Polyuria with dilute urine

Investigations