Diabetes insipidus

Question 1

What is diabetes insipidus?

Answer 1

A lack of (or lack of response to) ADH. This prevents the kidneys from being able to concentrate the urine, leading to polyuria and polydipsia.

Question 2

How is diabetes insipidus classified?

Answer 2

Cranial or nephrogenic

Question 3

What is nephrogenic diabetes insipidus?

What can cause this?

Answer 3

When the collecting ducts of the kidneys do not respond to ADH

Causes:

• Drugs, e.g. lithium
• Intrinsic kidney disease

Question 4

What is cranial diabetes insipidus?

What can cause this?

Answer 4

When the hypothalamus does not produce ADH for the pituitary gland to secrete

Causes:

• Tumour
• Trauma, e.g. injury, surgery
• Infection, e.g. meningitis/encephalitis

Question 5

Describe the typical pattern of urine vs. serum osmolality/osmolarity (which are essentially the same thing) in diabetes insipidus

Answer 5

• Low urine osmolality/osmolarity (dilute)

- High serum osmolality/osmolarity (concentrated)

Question 6

Which test is used to diagnose diabetes insipidus and differentiate between nephrogenic and cranial diabetes insipidus

Answer 6

Water deprivation/desmopressin stimulation test

desmopressin = synthetic ADH