Diabetes insipidus

Question 1

Causes of hypernatremia

Answer 1

Too little water/dehydration
The elderly
Terminal illness
Water loss > water intake
Excess Na +
IVT - too mcuh

Question 2

ADH action

Answer 2

Increased rabsoprtion of water
Increases bood volume and pressure
Decreases osmolality

Question 3

Types of diabetes insipidus

Answer 3

Cranial, nephrogenic

Question 4

What does the water deprivation test test for

Answer 4

Differentiates causes of diabetes insipidus
-Deprive patient of fluids to allow serum osmolality to rise and assess whether urine concentrates (increase osmolality)

Question 5

How is the water deprivation test carried out

Answer 5

Fasted overnight w fluids
Weight serum and urine osmolality measured reguarly
Test stopped early if >3% of body weight lost

Question 6

What is diabetes insipidus

Answer 6

Continued production of dilute urine despite fluid deprivation - failure to conserve water
results in the body being unable to concentrate urine as a result of either a lack of production of antidiuretic hormone (ADH) or a loss of sensitivity to ADH within the kidneys

Question 7

Plasma and urine osmolality in DI

Answer 7

High plasma Na and increased osmolality
Innapropriately low urine osmolality

Question 8

How diagnose DI

Answer 8

Water deprivation test
-Test urine osmolality after fluid deprived
-Give vasopressin (synthetic ADH) and measure again

Question 9

Which DI type would cause increased urine osmolality with vasopressin

Answer 9

eg <300 -> ADH -> >800 urine osmolality
ADH is being responded to but not enough is being released
CRANIAL DI

Question 10

What type of DI doesnt respond to ADH

Answer 10

Nephrogenic DI
<300 before and after ADH
- large volume of low osmolality urine
Kidney problem, not ADH level

Question 11

Water deprivation test primary polydipsia

Answer 11

> 800 before and after vasopressin

Question 12

Causes of cranial DI

Answer 12

Head trauma
Surgery
Tumours
Sarcoid
TB
Infections - meningitiis
Idiopathic
Familial - DIDMOAD

Question 13

DIDMOAD familial disease presentations

Answer 13

DI, DM, optic atrophy, deafness

Question 14

Features of cranial DI

Answer 14

Cerebral oedema
Hypernatremia
High serum osmolality, low urine
DDAV -> concentration of urine (pituitary issue)

Question 15

Causes of nephrogenic DI

Answer 15

Drugs - lithium
Chronic renal disease
Post obstructive uropathy
Metabolic - hypercalcemia, hypokalemia
Familial = X linked autosomal recessive

Question 16

Investigations

Answer 16

24 hour urine volume measurement - >3L = positive
Exclude DM and renal failure
Check electrolytes - Ca, K+
Water deprivation test
MRI brain for tumours
Serum ACE - sarcoidosis

Question 17

Treatment for nephrogenic DI

Answer 17

Correction of underlying cause
High doses of desmopressin trial
High fluid intake
THiazides and NSAIDs (decrease prostaglanding inhibition of ADH)

Question 18

Where does desmopressin need to be given

Answer 18

In hospital

Question 18

Symptoms of DI

Answer 18

Polyuria and polydipsia
Excessive thirst
Copious dilute urine
Nocturia
Symptoms associated with dehydration:
Fatigue
Dizziness
Weakness
Symptoms associated with a space-occupying lesion causing central DI may include:
Headache
Visual changes
Seizures

Question 19

Congenital causes of crainial DI

Answer 19

10%
Mutation in Arginine vasopressin-neurophysin II gene (AVP-NPII). This is autosomal dominant.
Wolfram syndrome. This is autosomal recessive.

Question 20

What to cover in DI history

Answer 20

Quantify fluid intake
Recent trauma or illness
A recent head trauma or surgery can cause central DI
Some illnesses may increase your risk of developing DI
Medications
Diuretics can cause polyuria
Lithium is a risk factor for developing DI
Family history
Some forms of DI are inherited

Question 21

What ratio is dilute urine confirming urine:serum ratio

Answer 21

Urine <2:1 to serum (less than twice as concentrated as serum)

Question 22

Water deprivation test and desmopressin stages

Answer 22

Stage 1 - Water deprivation
At the start of the test, the patient should empty their bladder and then have no fluids and only dry foods until the test is complete.
Hourly weights are taken.
2 hourly urine volume osmolality and volume.
4 hourly serum osmolality
Stage 2 - Desmopressin
Only proceed if urine is still dilute at end of the test (<600mOsmol/kg)
Administer desmopressin 2mcg IM or 20mcg intranasal.
Allow water consumption
Measure hourly urine osmolality for four hours.

Question 23

What protein can test for in DI

Answer 23

Serum copeptin
Equal levels as ADH in blood
Nephrogenic >21.4, central <4.9