Diabetes insipidus

Question 1

What is diabetes insipidius

Answer 1

Lack of ADH or a lack of response to ADH - prevents kidneys from being to concentrate the urine leading to polyuria and polydipsia

Question 2

Classification of diabetes insipidus

Answer 2

It can be classified as nephrogenic or cranial.

Question 3

What is primary polydipsia

Answer 3

Primary polydipsia is when the patient has a normally functioning ADH system but they are drinking excessive quantities of water leading to excessive urine production

Question 4

What is nephrogenic diabetes insipidus

Answer 4

Nephrogenic diabetes insipidus is when the collecting ducts of the kidneys do not respond to ADH

Question 5

Causes of nephrogenic diabetes insipidus

Answer 5

Lithium
Intrinsic kidney disease
Electrolyte disturbance(hypokalaemia and hypercalcaemia)

Question 6

Mutation associated with nephrogenic diabetes insipidus

Answer 6

Mutations in the AVPR2 gene on the X chromosome that codes for the ADH receptor

Question 7

What is cranial diabetes insipidus

Answer 7

Cranial diabetes insipidus is when the hypothalamus does not produce ADH for the pituitary gland to secrete

Question 8

Causes of cranial diabetes insipidus

Answer 8

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

Question 9

Presentation of diabetes insipidus

Answer 9

Polyuria (excessive urine production)
Polydipsia (excessive thirst)
Dehydration
Postural hypotension
Hypernatraemia

Question 10

IX for diabetes insipidus

Answer 10

Low urine osmolality
High serum osmolality
Water deprivation test(desmopressin stimulation test)

Question 11

Method of water deprivation test

Answer 11

Initially the patient should avoid taking in any fluids for 8 hours. This is referred to as fluid deprivation. Then, urine osmolality is measured and synthetic ADH (desmopressin) is administered.

8 hours later urine osmolality is measured again.

Question 12

What is gestational diabetes insipidus

Answer 12

During pregnancy, the placenta produces vasopressinase which breaks down vasopressin.

Gestational diabetes insipidus is therefore thought to be caused by the overproduction of vasopressinase by the placenta causing a deficiency of functional vasopressin.

Question 13

What is primary polydipsia

Answer 13

Characterised by an individual consuming large volumes of fluid and as a result producing large volumes of dilute urine

Most often primary polydipsia is due to a behavioural disorder.

Question 14

Ix interpretation - neurogenic DI

Answer 14

Urine osmolality after fluid deprivation - <300

Urine osmolality after desmopressin - >800

Question 15

Ix interpretation - nephrogenic DI

Answer 15

Urine osmolality after fluid deprivation - <300

Urine osmolality after desmopressin - <300

Question 16

Ix interpretation - Primary polydipsia

Answer 16

Urine osmolality after fluid fluid deprivation - >800

Urine osmolality after desmopressin >800

Question 17

Ix interpretation - partial cranial DI or nephrogenic DI or PP or diuretic abuse

Answer 17

Urine osmolality after fluid deprivation - <300

Urine osmolality after desmopressin - >800

Question 18

Mx of neurogenic diabetes insipidus

Answer 18

Desmopressin (orally, intranasally or parenterally)

Question 19

Risk with desmopressin treatment

Answer 19

Hyponatraemia

Question 20

Mx of nephrogenic diabetes insipidus

Answer 20

Access to drinking water

Correct metabolic abnormalities

Stop medications(lithium, demeclocycline)

High dose desmopressin sometimes for mild-to-moderate cases

Question 21

Mx of primary polydipsia

Answer 21

Management of underlying psychiatric condition

Question 22

Diabetes insipidus vs primary polydipsia

Answer 22

Less likely to experience dehydration

More likely to experience hyponatraemia as apposed to hypernatraemia

(in psychogenic)