Diabetes Insipidus

Question 1

What is DI.

Answer 1

The passage of large volumes (>3L/day) of dilute urine due to impaired water resorption by the kidney, because of reduced ADH secretion from the posterior pituitary (cranial DI) or impaired response of the kidney to ADH (nephrogenic DI).

Question 2

What does DI lead to. (2)

Answer 2

Polyuria.

Polydipsia.

Question 3

What are the two causes of DI.

Answer 3

Cranial.

Nephrogenic.

Question 4

What is cranial DI.

Answer 4

Failure of the posterior pituitary to produce vasopressin.

Question 5

What is nephrogenic DI.

Answer 5

Failure of the kidneys to respond to vasopressin.

Question 6

What are the causes of cranial DI. (7)

Answer 6

Idiopathic (

Question 7

What are the causes of nephrogenic DI. (4)

Answer 7

Metabolic (hypercalcaemia, hypokalaemia). 
Drugs (demeclocycline, lithium). 
Chronic renal disease. 
Inherited. 
Post obstructive uropathy.

Question 8

What investigations should be carried out in a patient with DI. (6)

Answer 8

Urine/plasma osmolality. 
Glucose (to exclude DM). 
UandEs. 
Plasma osmolites. 
Water deprivation test (in cranial DI urine osmolality will increase given desmopressin, no response in nephrogenic DI).

Question 9

What is the treatment for cranial DI.

Answer 9

Desmopressin (ADH analogue).

Question 10

What is the treatment for nephrogenic DI. (2)

Answer 10

Treat underlying cause. 
Thiazide diuretics (paradoxical effect, eg bendroflumethiazide).

Question 11

What are the symptoms of DI. (4)

Answer 11

Polyuria.
Polydipsia.
Dehydration.
Symptoms of hyponatraemia.

Question 12

What is the differential for DI. (4)

Answer 12

DM.
Lithium use.
Diuretics.
DI.