Diabetes insipidus

Question 1

Define diabetes insipidus

Answer 1

• The passage of large volumes (>3L/day) of dilute urine due to impaired water resorption by the kidney
• Due to reduced ADH secretion from the posterior pituitary (cranial DI) OR impaired kidney responce to ADH (nephrogenic DI)

Question 2

What are the symptoms of diabetes insipidus?

Answer 2

• Polyuria
• Polydipsia
• Dehydration
• Symptoms of hypernatraemia

Question 3

What are the causes of cranial DI?

Answer 3

• Idiopathic (~50%)
• Congenital defects in ADH gene
• Tumour (craniopharyngioma, metastases, pituitary tumour
• Trauma
• Hypophysectomy (surgical removal of hypophysis (pituitary gland))
• Inflam cell infiltration (histiocytosis, sarcoidosis
• Vascular issues (haemorrhage)
• Infection (meningoencephalitis)

Question 4

What are the causes of nephrogenic DI?

Answer 4

• Inherited
• Metabolic (low K+, high Ca2+)
• Drugs (lithium, demeclocycline)
• Chronic renal disease
• Post-obstructive uropathy

Question 5

How would you investigate DI?