Diabetes Insipidus Flashcards
What is diabetes insipidus?
Lack of ADH or lack of response to ADH
What does lack of ADH prevent kidney form doing?
Being able to concentrate urine leading tp polyuria and polydipsia
What are the classifications of diabetes insipidus?
Nephrogenic
Cranial
What is nephrogenic?
When collecting ducts of kidneys dont respond to ADH
What can cause nephrogenic Diabetes insipidus?
Drugs: Lithium for bipolar
AVPR2 Mutation on X chromosome: codes for ADH receptor
Intrinsic kidney disease
Electrolyte disorders
What is cranial diabetes insipidus?
When hypothalamus doesn’t produce ADH for pituitary gland to secrete
Causes of cranial diabetes?
Can be idiopathic or
- Brain tumours
- Head injury
- Brain malformations/infections
- Surgery/radiotherapy
Presnetation of diabetes insipidus?
- Polyuria
- Polydipsia
- Dehydration
- Postural hypotension
- Hypernatremia
Investigations of diabetes insipidus?
- Low urine osmolality
- High serum osmolality
- Water deprivation test
Water deprivation test AKA?
Desmopressin test
Method of desmopressin test?
- AVoid fluid for 8 hours
- Measure urine osmolality and administer synthetic ADH
- Measure osmolality 8 hours later again
Results for cranial diabetes insipidus desmopressin test?
Initially urine osmolality remains low as it continues to be diluted by XSive water secretion in kidneys
When synth ADH is given, kidneys respond & reabsorb water, concentrating urine= High osmolality
Why the results occur that way in cranial diabetes insipidus?
Patient lacks ADH
Kidneys can still respond to it
Nephrogenic respose to desmopressin test?
Low osmolarity (diluting urine with XSive water from kidneys)
Remains low after synthetic ADH as well
Why the results occur that way in nephrogenic diabetes insip?
Patient unable to respond to ADH
