Diabetes insipidus Flashcards
What are the 2 types of diabetes insipidus
Cranial - inadequate secretion of vasopressin
Nephrogenic - insensitivity to vasopressin
What are causes of Cranial DI
pituitary tumour/surgery
traumatic brain injury
infection
sarcoidosis/TB
Haemochromatosis
What are causes of nephrogenic diabetes insipidus
lithium therapy
electrolyte imbalance
idiopathic
ureteric obstruction
Inherited ( AVPV2 gene )
What would a patient with DI present with
polyuria
nocturia
polydipsia
dehydration– tachycardia, reduced turgor, dry mucous membranes
signs relating to cause – bitemporal hemianopia
What investigations are required
U &Es - raised calcium , raised urea, low potassium , normal sodium, normal glucose
plasma osmolality= high
urine osmolality =low
What is the water deprivation test
Water restricted for 8 hours- measure plasma ad urine osmolality every hour , then give desmopressin and measure urine osmolality
Cranial - if >50% rise in osmolality after desmopressin
Nephrogenic -<45% rise in urine osmolality after desmopressin
When do you stop the water deprivation test
if body weight falls by 3%
What is management for DI
treat underlying cause
Cranial - intranasal desmopressin
Nephrogenic - thiazide diuretics/NSAIDs, low salt/protein diet
What results would be seen in water deprivation test in a normal patient
plasma osmolarity at start - normal
final urine osmolarity >600
urine osmolarity post DDAVP- >600
What results would be seen in water deprivation test for a patient with psychogenic polydipsia
starting plasma osmolarity - low
final urine osmolarity >400
urine osmolarity post DDAVP >400
What results would be seen in water deprivation test for a patient with cranial DI
Starting plasma osmolarity - high
final urine osmolarity - <300
after DDAVP- >600
What results would be seen from water deprivation test in a patient with nephrogenic DI
starting plasma osmolarity - high
final urine osmolarity - <300
post DDAVP- <300
