Diabetes Insipidus Flashcards
What is diabetes insipidus?
Lack of ADH or lack of response to ADH –> kidneys unable to concentrate the urine –> polyuria + polydipsia
How is DI classified?
Nephrogenic or cranial
What causes nephrogenic DI?
Collecting ducts do not respond to ADH:
- lithium
- mutations in AVPR2 gene on X chromosome
- intrinsic kidney disease
- hypokalaemia
- hypercalcaemia
What causes cranial DI?
Hypothalamus does not produce ADH for pituitary gland to secrete:
- brain tumours
- head injury
- brain malformations
- brain infections
- brain surgery/RT
- idiopathic
How does DI present?
Polyuria Polydipsia Dehydration Postural hypotension HYPERnatraemia
How should DI be investigated?
Water deprivation test
Low urine osmolality
High serum osmolality
What is the water deprivation test also known as?
Desmopressin stimulation test
How is the water deprivation test carried out?
Patient should avoid drinking any fluids for 8 hours (fluid deprivation)
Then urine osmolality is measured + synthetic ADH (desmopressin) measured
8 hours later urine osmolality is measured again
What would the results of the water deprivation test be in cranial DI?
Initial urine osmolality would be low
After synthetic ADH, urine osmolality would be high
(because problem is lack of ADH)
What would the results of the water deprivation test be in nephrogenic DI?
Urine osmolality will remain low, even after the synthetic ADH
If the urine osmolality is high initially, after 8 hours of water deprivation, what does this indicate?
No diabetes insipidus
–> the patient is probably just drinking too much (primary polydipsia)
How is DI managed?
Treat underlying cause if possible Cranial DI: - desmopressin (synthetic ADH) Nephrogenic DI: - high dose desmopressin can be used under close monitoring
