Diabetes Insipidus Flashcards
what is the def of DI
a disorder of inadequate secretion/insensitivity to vasopressin (ADH) causing hypotonic polyuria
what is the aetiology of DI
central/cranial
-failure of ADH secretion by posterior pituitary
nephrogenic
-insensitivity of collecting duct to ADH
water channels (aquaporins) fail to activate and the luminal membrane of the collecting duct remains impermeable to water therefore water is not reabsorbed and there is hypotonic polyuria which causes polydipsia
what are the causes of central/cranial DI
idiopathic tumours (pituitary) infiltrative (sarcoidosis) infection (meningtitis) trauma
what are the causes of nephrogenic DI
idiopathic drugs (lithium) pyelonephritis pregnancy osmotic diuresis (DM)
what is the epi of DI
median onset is 24yrs
history of DI
polyuria, nocturia, polydipsia
examination of DI
cranial DI has few symptoms with adequate fluids
urine output >3l/24h
fluid intake
what are the investigations performed in suspected DI
bloods -UEs & Ca -Na may rise secondary to dehydration -high plasma osmolality -low urine osmolality water deprivation test -water restricted for 8h -plasma & urine osmolality measured every hour -desmopressin given after 8h and urine osmolality is measured
water deprivation - normal
rise in plasma osmolality and ADH secretion
causes increased water reabsorption in collecting ducts
urine is concentrated (>600mosmol/kg)
water deprivation - DI
lack of ADH activity means urine is not concentrated by collecting ducts
<400mosmol/kg
cranial - urine osmolality >50% rise with desmopressin
nephrogenic - urine osmolality <45% rise with desmopressin
what is the management of DI
treat cause cranial DI -desmopressin (vasopressin analogue) -carbamazepine in mild disease nephrogenic DI -Na &/or protein restriction can help polyuria -thiazide diuretics
complications of DI
hypernatraemic dehydration
excess desmopressin may cause hyponatraemia
prognosis of DI
dependent on cause
cure of cranial/nephrogenic may be possible with removal of cause
