Diabetes Insipidus Flashcards
what is diabetes insipidus?
lack of antidiuretic hormone (ADH) or a lack of response to ADH
how does diabetes insipidus impact the body?
prevents the kidneys from being able to concentrate the urine leading to polyuria and polydipsia
what is primary polydipsia?
patient has a normally functioning ADH system but they are drinking excessive quantities of water leading to excessive urine production
what is nephrogenic diabetes insipidus?
collecting ducts of the kidneys do not respond to ADH
name some causes of nephrogenic diabetes inspidus
- drugs - lithium
- mutations in the AVPR2 gene
- intrinsic kidney disease
- electrolyte disturbance (hypokalaemia and hypercalcaemia)
what is cranial diabetes insipidus?
hypothalamus does not produce ADH for the pituitary gland to secrete
what are the causes of cranial diabetes insipidus?
- idiopathic
- brain tumours
- head injury
- brain malformations
- brain infections (meninigitis, encephalitis, tuberculosis)
- brain surgery or radiotherapy
how does diabetes insipidus present?
- polyuria
- polydipsia
- dehydration
- postural hypotension
- hypernatraemia
what investigations are done in diabetes insipidus?
- low urine osmolality
- high serum osmolality
- water deprivation test
what is the test of choice for diagnosing diabetes insipidus?
water deprivation test
how is a water deprivation test undertaken?
- patient should avoid any fluids for 8 hours
- urine osmolality is measured
- synthetic ADH (desmopressin) is administered
- 8 hours later urine osmolality is re-measured
explain the water deprivation results in cranial diabetes insipidus
patient lack ADH but kidneys are still capable of responding to ADH
* urine osmolality = low (continues to be diluted by excessive water secretion in the kidneys)
* post-desmopression urine osmolality = high (kidneys respond by reabsorbing water and concentrating the urine)
explain the water deprivation results in nephrogenic diabetes insipidus
kidneys are unable to respond to ADH
* urine osmolality = low (continues to be diluted by excessive water secretion in the kidneys)
* post-desmopression urine osmolality = low (kidneys havent responded and are still secreting excessive water)
explain the water deprivation results in primary polydispsia
- urine osmolality = high
- post-desmopressin urine osmolality = high
what is the role of desmopressin in the management of diabetes insipidus?
- cranial = replace ADH
- nephrogenic = higher doses under close monitoring
