Diabetes Insipidus Flashcards
What is diabetes insipidus?
Caused by a lack of ADH or a lack of response to ADH.
What is the role of ADH?
It acts on the collecting ducts and allows them to reabsorb water from the urine.
How does diabetes insipidus work>
It prevents the kidneys from being able to concentrate the urine, leading to polyuria and polydipsia.
What is nephrogenic diabetes insipidus?
When the collecting ducts of the kidneys don’t respond to ADH that’s in the blood stream.
What causes nephrogenic diabetes insipidus?
Lithium
Genetics
Any chronic kidney diseaseHypokalaemia
Hypercalcaemia
What is cranial diabetes insipidus?
When the hypothalamus doesn’t produce enough/any antidiuretic hormone for the posterior pituitary gland to release
What causes cranial diabetes insipidus?
idiopathic brain tumours head injuries brain malformations meningitis encephalitis TB radiotherapy brain surgery
What is primary polydipsia?
when someone has normal ADH production and normal functioning kidneys but drinks too much water leading to polyuria and polydipsia
What are the signs of diabetes insipidus?
polyuria polydipsia dehydration postural hypotension hypernatraemia (concentrated blood) low urine osmolality High serum osmolality
What test can diagnose diabetes insipidus?
Water deprivation test (desmopressin stimulation test)
avoid food or fluid for 8hrs before test; urine osmolality is measured; then synthetic ADH is given; urine osmolality is measured again after 8hrs.
MEASURES URINE OSMOLALITY
What does the test show for cranial, nephrogenic and primary polydipsia?
Cranial: 1st test low, 2nd test high (because the patient can respond to the ADH
Nephrogenic: 1st test low, 2nd test low.
Primary polydipsia: 1st test high, 2nd test high (since the first test is high you don’t need to keep going with the test).
What is the treatment for diabetes insipidus?
Desmopressin
Has to be given in very high doses for nephrogenic diabetes insipidus.
