Diabetes Insipidus Flashcards
What defines diabetes insipidus?
Over 3 litres of dilute urine produced daily
Low ADH secretion/action
What are the 2 types of diabetes insipidus?
Cranial (low ADH secretion)
Nephrogenic (low kidney response to ADH)
What can cause cranial diabetes insipidus?
ADH gene mutation
Pituitary adenomas
Brain tumours
Head injuries
Infections (TB, encephalitis, meningitis)
Radiotherapy
Idiopathic
What can cause nephrogenic diabetes insipidus?
ADH-R mutation (AVPR2 gene on X chromosome)
Drugs eg lithium
Intrinsic kidney disease
Hypokalaemia
Hypercalcaemia
In diabetes insipidus, low levels of ___ causes large ____ of _____ urine
ADH
volume
dilute
What are symptoms of diabetes insipidus?
Polyuria
Polydipsia
Hypernatremia (high conc as not much water)
Lethargy
Confusion
Coma
Severe dehydration
When should you suspect diabetes insipidus?
Over 3 litres of urine produced in 24 hours
What is the water deprivation test for diabetes insipidus?
No fluid for 8 hours.
Urine osmolality then measured.
Desmopressin given.
Wait 8 hours
Measure urine osmolality again.
In cranial DI, first reading will show low urine osmolality but after desmopressin, kidneys will respond and absorb water so urine will be concentrated and have high osmolality.
In nephrogenic DI, first reading will show low urine osmolality and after given desmopressin, still low urine osmolality as nephron doesn’t respond.
What is a differential diagnosis to diabetes insipidus in patient with polydipsia and polyuria?
Primary polydipsia
(can tell with water deprivation test the urine osmolality will be high after first 8 hours before synthetic ADH given so can’t be DI)
How do you treat cranial diabetes insipidus?
Desmopressin
How do you treat nephrogenic diabetes insipidus?
Thiazides
Treat underlying cause
(thiazides increase H2O loss at DCT so encourages sodium uptake (?) and therefore water retention. This concentrates urines and increases water in plasma.)
