Diabetes Insipidus Flashcards
What is the basic pathophysiology of diabetes insipidus?
Cranial - reduced ADH production
Nephrogenic - reduces response to ADH
No action of ADH on V1 receptors (no vasoconstriction of vascular smooth muscle), no action on V2 receptors in nephron DCT and CD (leads to no insertion of aquaporins – unable to reabsorb water)
What are the common causes of cranial diabetes insipidus?
lack of ADH production by the hypothalamus.
This may be idiopathic
Secondary to brain insult (tumour, trauma, surgery)
Genetic mutation in ADH gene (AD) Wolfram syndrome (DI, optic atrophy, deafness and diabetes mellitus)
What are some causes of nephrogenic diabetes inspidus?
collecting ducts do not respond to ADH
Idiopathic
Drugs (lithium)
Genetic mutation in ADH receptor gene (x-linked recessive) Hypercalcemia and hypokalemia Kidney disease.
What are the signs and symptoms of Diabetes Insipidus?
Polyuria (large volumes of dilute urine 3000ml per day)
Nocturia
Polydipsia – due to thirst mechanism
Dehydration - dizziness, headache,
Postural hypotension
What investigations should be done for diabetes insipidus?
Low urine osmolarity
High/normal serum osmolarity – fluid loss is normally balanced by intake
Urine output>3000ml/24hr
Water deprivation test
How is the water deprivation test carried out?
Patient avoids fluid for 8hrs so is in water deprivation.
Urine osmolarity is then measured, the patient is then given synthetic ADH – desmopressin and urine osmolarity measured again over next 2-4hrs
What do the results of the water deprivation test indicate in relation to diabetes insipidus?
What is the common treatment for diabetes insipidus?
ADH (vasopressin) IM/SC injection to replace endogenous in cranial DI
Nephrogenic – inc water access, high dose desmopressin, thiazide diuretics, NSAIDs
Desmopressin (vasopressin analogue) - DI and nocturnal enuresis in children – risk of hyponatreaemia
