Diabetes insipidus

Question 1

What is central diabetes insipidus?

Answer 1

1. most common form of diabtetes insipidus

2. insufficient ADH released from hypothalamus

Question 2

What is nephrogenic diabetes insipidus?

Answer 2

1. defective ADH receptors in the kidne

2. kidneys do not repond to ADH

Question 3

cause of central diabetes insipidus?

Answer 3

1. idiopathic

2. brain tumor/brain injury / pituitary ischaemia

Question 4

cause of nephrogenic diabetes insipidus?

Answer 4

1. adverse effect of medication - lithium
2. hypokalaemia
3. hypercalcaemia

Question 5

What is the physiology of ADH?

Answer 5

1. ADH enables to integration of aquaporins in the membrane of collecting duct cells
2. reabsorbtion of excess water in the urine

Question 6

Name 4 clinical features of diabetes insipidus?

Answer 6

1. polyuria with dilute urine
2. nocturia
3. polydipsia- excess thirst
4. dehydration

Question 7

Ix - describe the ‘water deprivation test’

Answer 7

1. patient stop drinking water
2. test urine volume and osmolality of urine - every 1 hour
3. test sodium and plasma osmolality every 2 hours

Question 8

Ix - result of water deprivation test - Primary polydipsia

Answer 8

1. urine osmolality rises and reaches normal value

Question 9

Ix - result of water deprivation test - Diabetes inspidius

Answer 9

1. no change in urine osmolality even with rising plasma osmolality
2. plasma osmolality is very high

Question 10

Ix - How is central vs nephrogenic diabestes insipidus differentiated

Answer 10

1. administer desmopressin
   - CDI : urine osmolality rises after desmopressing admin
   - NDI - urine osmolalty remains low after desmopressin

Question 11

Tx of CDI

Answer 11

1. Desmopressin

Question 12

Tx of NDI

Answer 12

1. discontinuation of the causatve agent
   - lithium etc
2. Thiazide diuretics