Diabetes Insipidus

Question 1

What is Diabetes insipidus ?

What does it lead to?

Answer 1

a lack of ADH or lack of response to ADH

This prevents the kidneys from being able to concentrate the urine leading to polyuria (excessive amount of urine) and polydypsia (excessive thirst)

Question 2

What are the two classifications of Diabetes insipidus?

Answer 2

Nephrogenic (insenitivity to ADH - dont respond)

Cranial (deficiency of ADH due to hypothalamus not producing enough)

Question 3

What is primary polydypsia?

Answer 3

psychiatric: when a patient has normal functioning ADH system but they are drinking excessive water leading to excess urine production

Question 4

What are causes of nephrogenic DI

Answer 4

Causes of nephrogenic DI

1. genetic: more common form affects the vasopression (ADH) receptor, less common form due tomutation in the gene that encodes the aquaporin 2 channel
2. electrolytes: hypercalcaemia, hypokalaemia
3. drugs: LITHIUM** demeclocycline,
4. tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis

Question 5

What are causes of Cranial DI?

Answer 5

Brain tumours - Craniopharyngiomas
Head injury
Brain malformations
Brain infections (meningitis, encephalitis and tuberculosis)
Brain surgery or radiotherapy
Haemochromatosis

Question 6

What are the features of diabetes insipidus?

Answer 6

polyuria
polydipsia
hypernatraemia
dehydration and postural hypotension

Question 7

What investigation findings would you see in diabetes insipidus?

Answer 7

1. high plasma osmolality,

2.low urine osmolality
- a urine osmolality of >700 mOsm/kg excludes
diabetes insipidus

3. water deprivation test

Question 8

Which is the main test for diagnosing DI and what is it also known as?

Answer 8

Water deprivation test

also known as desmopressin stimulation test

Question 9

How do you interpret the results of the water deprivation test?

Answer 9

Urine osmolality:

Cranial Insipidus - after water deprivation: low, after ADH - high

Nephrogenic insipidus - after water deprivation: low, after ADH - remains low

Primary polydypsia: after water deprivation: high, after ADH - high

high urine osmolality after water deprivation proves there is no diabetes insipidus

Question 10

How do you manage diabetes insipidus?

Answer 10

if possible treat underlying cause
mild cases to be managed conservatively

Desmopressin - synthetic ADH can be used

• in cranial: to replace ADH
• in nephrogenic - in higher doses under close monitoring