Diabetes Insipidus Flashcards
1
Q
Two types of DI
A
- Cranial - vasopressin deficiency
- Nephrogenic - vasopressin resistance
2
Q
What does DI lead to?
A
Passing large volumes of dilute urine with profound unquenchable thirst
3
Q
Biochemical hallmarks of DI
A
- High serum osmolarity
- Low urine osmolarity
- High urine volume
Severe cases:
* Hypernatraemia
* Dehydration
* Death
4
Q
Cranial DI
A
- Pituitary disease
- Strong FH
5
Q
Nephrogenic DI
A
- Caused by metabolic and electrolyte disturbance
- Renal disease
- Drugs affecting kidney
6
Q
What is primary polydipsia?
A
- Behavioural condition
- Leading to polydipsia
- = Drives polyuria
- NOT associated with hypernatraemia
- But could lead to dilutional hyponatraemia
7
Q
What can happen in some with primary polydipsia?
A
- Impaired ability to concentrate urine
- Due to down regulation of vasopressin release
- Occasionally can make it difficult to distinguish primary polydipsia from partial DI
8
Q
Investigations DI
A
- Urine volume more than 3L in 24hrs
- High serum osmolarity - more than 295mosmol/kg
- Low urine osmolarity - less than 300mosmol/kg
- Water deprivation test
9
Q
Exlcusion criteria for DI urine and serum mosmol
A
- Exclude if urine osmolarity more than 600 mosmol/kg
- Or double serum osmolarity
10
Q
When to use water deprivation test?
A
- In partial DI
- When DI is not clinically obvious
11
Q
What will happen to pts with frank DI in water deprivation test?
A
- Unacceptable thirst
- Lose significant weight due to water loss
- Needs to be stopped if weight loss occurs or symptoms too severe
12
Q
Water deprivation test results for exclusion
A
- If urine osmolarity is more than 600mosmol/kg
- serum osmolarity remains less than 300mosmol/kg
- = exclude
13
Q
What is given in second part of WDT?
A
- Synthetic vasopressin is given (DDAVP, desmopressin)
- In cranial DI, vasopressin leads to reduced urine volume and increased urine osmolarity
- In nephronic there is no response
14
Q
Another, newer test to confirm DI
A
- Co-peptin
- = AVP (vasopressin) precursor
15
Q
Management of cranial DI
A
- Investigate for pituitary disease
- Desmopressin (DDAVP) can be intranasally, orally, sublingually or paraenterally.
16
Q
What can overtreatment with desmopressin lead to?
A
- Dilutional hyponatraemia
- –> headache, reduced cognition, seizures if sudden drop
17
Q
Signs of undertreatment of desmopressin
A
- Excessive thirst
- Polyuria
18
Q
Why can pts sometimes with DI not be thirsty?
A
- Impaired thirst mechanism if hypothalamus involved
- = hypodipsic DI
- eg in hypothalamic infiltrative disorders
- = risk of severe dehyration and hypernatraemia
19
Q
Nephrogenic DI management
A
- Underlying cause considered and reversed if possible
- If not, drink according to thirst and keep up with water loss
- Low salt
- Low protein diet
- Diuretics
- NSAIDs
20
Q
A
