Diabetes insipidus Flashcards
Causes of hypernatremia
Too little water/dehydration
The elderly
Terminal illness
Water loss > water intake
Excess Na +
IVT - too mcuh
ADH action
Increased rabsoprtion of water
Increases bood volume and pressure
Decreases osmolality
Types of diabetes insipidus
Cranial, nephrogenic
What does the water deprivation test test for
Differentiates causes of diabetes insipidus
-Deprive patient of fluids to allow serum osmolality to rise and assess whether urine concentrates (increase osmolality)
How is the water deprivation test carried out
Fasted overnight w fluids
Weight serum and urine osmolality measured reguarly
Test stopped early if >3% of body weight lost
What is diabetes insipidus
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
Plasma and urine osmolality in DI
High plasma Na and increased osmolality
Innapropriately low urine osmolality
How diagnose DI
Water deprivation test
-Test urine osmolality after fluid deprived
-Give vasopressin (synthetic ADH) and measure again
Which DI type would cause increased urine osmolality with vasopressin
eg <300 -> ADH -> >800 urine osmolality
ADH is being responded to but not enough is being released
CRANIAL DI
What type of DI doesnt respond to ADH
Nephrogenic DI
<300 before and after ADH
- large volume of low osmolality urine
Kidney problem, not ADH level
Water deprivation test primary polydipsia
> 800 before and after vasopressin
Causes of cranial DI
Head trauma
Surgery
Tumours
Sarcoid
TB
Infections - meningitiis
Idiopathic
Familial - DIDMOAD
DIDMOAD familial disease presentations
DI, DM, optic atrophy, deafness
Features of cranial DI
Cerebral oedema
Hypernatremia
High serum osmolality, low urine
DDAV -> concentration of urine (pituitary issue)
Causes of nephrogenic DI
Drugs - lithium
Chronic renal disease
Post obstructive uropathy
Metabolic - hypercalcemia, hypokalemia
Familial = X linked autosomal recessive
Investigations
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
Treatment for nephrogenic DI
Correction of underlying cause
High doses of desmopressin trial
High fluid intake
THiazides and NSAIDs (decrease prostaglanding inhibition of ADH)
Where does desmopressin need to be given
In hospital
Symptoms of DI
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
Congenital causes of crainial DI
10%
Mutation in Arginine vasopressin-neurophysin II gene (AVP-NPII). This is autosomal dominant.
Wolfram syndrome. This is autosomal recessive.
What to cover in DI history
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
What ratio is dilute urine confirming urine:serum ratio
Urine <2:1 to serum (less than twice as concentrated as serum)
Water deprivation test and desmopressin stages
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.
What protein can test for in DI
Serum copeptin
Equal levels as ADH in blood
Nephrogenic >21.4, central <4.9
