Diabetes Insipidus Flashcards
What are the 2 types of diabetes inspidius?
- cranial/central
2. nephrogenic
What happens in cranial DI?
reduced synthesis or release of AVP from posterior pituitary
What is AVP also called?
ADH and desmopressin
What happens in nephrogenic DI?
collecting ducts insensitivity to AVP (ADH)
What happens in DI?
formation of inappropriately hypotonic (dilute) urine
What type of DI is more common?
cranial
What are RF for cranial DI?
- Pituitary surgery
- Craniopharyngioma
- Pituitary stalk lesions
- Traumatic brain injury
- Congenital pituitary malformation
- History of autoimmune disordered
- Infection (meningitis)
- Sarcoidosis
What are RF for nephrogenic DI?
- FHx: X linked or autosomal recessive
- History of lithium therapy: 40% patients develop
- Chronic renal disease
- High Ca+
- Low K+
- Idiopathic
What gene puts you at risk of nephrogenic DI?
AVPV2
What are symptoms and signs of DI?
- polydipsia
- polyuria
- nocturia
- Dehydration: tachycardia, reduced tissue turgor/ dry mucous membranes
- Signs of cause e.g. bitemporal hemiopia
What are possible DDx of DI?
- Psychogenic polydipsia
- DM
- Diuretic use
- Hypercalcaemia
What test is used to confirm DI?
water deprivation test
What investigations are used for DI?
- Urine osmolality
- Serum osmolality
- Serum glucose, sodium, potassium, calcium, urea
- Urine dipstick
- 24hr urine collection for volume
- Water deprivation test
- AVP (desmopressin) stimulation test
- Hypertonic saline-stimulated test with measurement of copeptin
What is urine osmolality in DI like?
low
How much urine may be collected in in 24hr for DI?
> 3L in 24hr
How does cranial DI react to water deprivation test?
- urine osm <400, no ADH released so no concentration of urine in water derp
- with desmopressin rapid concertation of urine, urine osm increased >50%
How does nephrogenic DI react to water deprivation test and stim?
- ADH insesntivity so no concetration of urine urine osm <400 in water dep
- and with desmopressin urine osm increases by <45%, urine remains unconcentrated
How would you treat hyperatraemia at any stage of DI?
1st line: oral / IV fluids
How do you treat cranial DI?
1st line: desmopressin (intranasal)
adults: 0.1 to 1 mg/day orally given in 2-3 divided doses
MRI head
How do you treat nephrogenic DI?
1st line: maintenance adequate fluid intake and sodium restriction e.g. hydrochlorothiazide thiazide diuretic or NSAIDs
Why may you give NSAIDs for DI?
NSAIDs inhibit prostaglandin synthase and prostaglandin inhibits ADH
What are possible complications for DI?
- Hypernatremia
- Thrombosis
- Bladder and renal dysfunction
- Iatrogenic hyponatraemia
What are urine and plasma conc in DI?
- Urine osmolality: low (>700 exclude DI)
2. Plasma osmolality high
How does normal person react to WDT?
- rise in ADH so increase in urine osmolality >600 in water derp (concentrated(
- No change in osmolalities no more water to reabsorb with desmopressin
What is the process of the water deprivation test?
- Water restricted for 8 hours
- Plasma and urine osmolality are measured ever hour
- After 8 hours give desmopressin (ADH analogue) and measure urine osmolality
What happens during water deprivation?
- Water deprivation
- Leads to increased serum osmolality
- So osmoreceptors are simulated
What happens when osmoreceptors are simulated?
- Therefore the posterior pituitary released vasopressin (ADH)
- Leads to increased water reabsorption from renal collecting ducts
- So reduce urine volume, increase in urine osmolality
- Reduction in serum osmolality
How is secretion of ADH simulasted?
raised serum osmolality or low blood pressure
Where does ADH act?
V2 receptors on the cells of the distal convoluted tubule/collecting duct
What does ADH do?
- Increases aquaporin expression on the apical membrane of these cells, which makes them more permeable, allowing reabsorption of water into the blood
- This concentrates the urine, and reduces the osmolality of the blood
