Diabetes Insipidus

Question 1

What is diabetes insipidus?

Answer 1

It is a condition characterised by the passage of large volumes of dilute urine due to either reduced secrection of ADH from the posterior pituitary or impaired kidney response to ADH. Both of which results in impaired water reabsorption of water in the kidney.

Question 2

What are the symptoms of diabetes insipidus?

Answer 2

Polyuria
Polydipsia - this can be all consuming and uncontrollable
Dehydration
Symptoms of hypernatraemia

Question 3

What are the different types of diabetes insipidus?

Answer 3

Cranial - problem arises from the posterior pituitary or hyperthalamus
Nephrogenic - Impaired kidney response to ADH
Gestational - occurs only during pregnancy
Dipsogenic - Caused by abnormal thirst mechanisms in the hypothalamus

Question 4

What are the causes of cranial diabetes insipidus?

Answer 4

Idiopathic - 50%

Congenital - Defects in ADH gene

Tumour

Trauma - hypophysectomy

Autoimmune hypophysitis

Infiltrations

Vascular - haemorrhage

Infection

Question 5

Causes of nephrogenic diabetes insipidus?

Answer 5

Inherited
Metabolic - low potassium, high calcium
Drugs - Lithium, demeclocycline
Chronic renal disease
Post-obstructive uropathy

Question 6

How is diabetes insipidus diagnosed?

Answer 6

Glucose blood test - exclude diabetes mellitus
U&Es
Calcium levels
Serum and urine osmolalities

The 8 hr water deprivation test - aims to see if the kidneys continue to produce dilute urine despite dehydration

Question 7

How is cranial diabetes insipidus treated?

Answer 7

Find the cause - MRI head scan
Test pituitary function
Desmopression which is a synthetic analogue of ADH

Question 8

How is nephrogenic diabetes insipidus treated?

Answer 8

Treat the cause
If it persist try bendroflumethiazide
NSAIDs may be helpful

Question 9

How would NSAIDs help in the treatment of diabetes insipidus?

Answer 9

They lower urine volume and plasma sodium concentration by inhibiting inhibit prostaglandins which locally inhibit the action of ADH - so they inhibit ADH’s inhibition

Question 10

How would you manage an emergency diabetes insipidus event?

Answer 10

1) Urgent U&Es
2) Urgent serum and urine osmolalities
3) Monitor urine output
4) Check U&Es twice daily
5) Intravenous infusion (IVI) to keep up with urine output - Lower Na+ slowly
6) Desmopressin