Diabetes insipidus Flashcards
What is diabetes insipidus, and what does this lead to?
Lack of ADH or a lack of response to ADH which means that the kidneys can’t concentrate urine resulting in polyuria and polydipsia
What are the 2 classifications of diabetes insipidus?
Nephrogenic and cranial
1) What is the problem in nephrogenic diabetes insipidus?
2) Name 2 causes of this
1) The collecting ducts of the kidneys do not respond to ADH
2) Intrinsic renal disease, drugs (lithium), electrolyte imbalances (low K+, high Ca2+), mutations of the gene that codes for ADH
1) What is the problem in cranial diabetes insipidus?
2) Name 2 causes of this
1) Hypothalamus does not produce ADH for the pituitary gland to secrete
2) Idiopathic, brain tumour, brian injury, brain surgery, brain malformations, brain infections
1) Name 2 ways diabetes insipidus can present
2) Name 2 investigations
1) Polyuria, polydipsia, hypernatraemia, postural hypotension, dehydration
2) Water deprivation test, urine osmolality, serum osmolality
The water deprivation test is the diagnostic test of choice - how does it work?
Patient should avoid taking in any fluids for 8 hours. Then, urine osmolality is measured and synthetic ADH is administered. 8 hours later urine osmolality is measured again
Water deprivation test results:
1) What would be seen in cranial diabetes insipidus?
2) What would be seen in nephrogenic diabetes insipidus?
1) Patient lacks ADH but the kidneys are still capable of responding to ADH therefore the urine osmolality is low. When synthetic ADH is given the kidneys respond by reabsorbing water and concentrating the urine so the urine osmolality will be high
2) Patient is unable to respond to ADH. They are diluting their urine with the excessive water secretion by the kidneys. Therefore the urine osmolality will be low initially and remain low even after the synthetic ADH is given
Name a synthetic ADH that can be used to manage diabetes insipidus
Desmopressin
