DIABETES INSIPIDUS

Question 1

WHAT IS DIABETES INSIPIDUS?

Answer 1

Metabolic disorder characterised by the inability to produce concentrate urine leading to production of large quantities of dilute urine

Question 2

WHAT ARE THE 2 TYPES OF DIABETES INSIPIDUS?

Answer 2

1) Central - hypothalamic/ pituitary disorder resulting in reduced synthesis or release vasopressin
2) Peripheral - renal insensitivity to vasopressin

Question 3

WHAT ARE THE CAUSES OF:

1) CENTRAL DI
2) PERIPHERAL DI

Answer 3

1) Pituitary surgery/ traumatic brain injury/ SAH

2) CKD/ lithium therapy

Question 4

WHAT ARE THE CHARACTERISITIC FEATURES OF DI?

Answer 4

1) Polydipsia - unquenchable thirst
2) Polyuria
3) Dilute urine

Question 5

WHAT ARE THE BIOCHEMICAL HALLMARKS OF DI?

Answer 5

1) High serum osmolality
2) Low urine osmolality
3) In severe cases, hypernatraemia

Question 6

HOW IS DI CONFIRMED?

Answer 6

High urine volume with high serum osmolality and low urine osmolality

Question 7

WHAT IS THE MANAGEMENT OF CENTRAL DI?

Answer 7

1) Investigate for pituitary disease

2) Desmopressin administered intra-nasally, orally, sublingually or parenterally.

Question 8

WHAT IS THE MANAGEMENT OF PERIPHERAL DI?

Answer 8

1) Underlying cause should be treated
2) Low salt and low protein diet
3) Drink according to thirst and keep up with water loss
4) Thiazide like diuretics - Di causes more excretion of water than sodium this causes polydipsia to dilute serum back to normal. thiazide diuretics prevent reabsorption of Na+ and Cl- from DCT.

Question 9

WHAT IS THE MANAGEMENT FOR HYPERNATRAEMIA?

Answer 9

• Oral fluids or IV 5% dextrose or 0.8% saline

Question 10

WHAT IS THE TEST FOR DI AND WHAT DOES IT INVOLVE?

Answer 10

• Water deprivation test
• Distinguishes if patient has DI or other causes of polydipsia
• Involves not drinking water for several hours. Test measures changes in bodyweight, urine output and composition. If there is no change in water loss despite fluid deprivation then desmopressin is administered to determine if it is central or peripheral. Central urine osmolality will increase and peripheral there will be no change.