Diabetes Insipidus Flashcards
What is diabetes insipidus?
A lack of ADH or a lack of response to ADH
What is the action of ADH?
ADH acts on the collecting duct of the kidneys, to allow reabsorption of water
What is nephrogenic diabetes insipidus?
Where the collecting ducts of the kidneys do not respond to ADH, and water is not reabsorped
What is primary polydipsia?
Where the patient has normal and functioning ADH, but is drinking excessive amounts of water, causing polyuria
What are the causes of nephrogenic diabetes insipidus?
Medications - lithium
Genetic mutations in the ADH receptor gene
Hypercalcaemia
Hypokalaemia
Kidney diseases
What is cranial diabetes insipidus?
Where the hypothalamus gland does not produce ADH for the pituitary gland to secrete
What are the causes of cranial diabetes insipidus?
Idiopathic
Brain tumours
Brain surgery
Meningitis/ encephalitis
Genetic mutations in ADH gene
Wolfram syndrome
What is the presentation of diabetes insipidus?
Polyuria
Polydipsia
Dehydration
Postural hypotension
Hypernatraemia
What investigations are performed in diabetes insipidus?
U&Es - hypernatremia
Urine osmolality - low (low concentration of solutes)
Serum osmolality - high
What is the investigation of choice for diagnosis of diabetes insipidus?
Water deprivation test (desmopressin stimulation test)
How is the water deprivation test performed?
The patient is fluid deprived for 8 hours before the rest
- Urine osmolality is measured, and desmopressin is given
- Urine osmolality is measured again 8 hours later
How are the results of the water deprivation test interpreted?
Cranial DI
- Low osmolality after deprivation
- High osmolality after desmopressin
Nephrogenic
- Low osmolality after deprivation
- Low osmolality after desmopressin
Primary polydipsia
- High osmolality after deprivation - no diabetes insipidus
What is the management of diabetes insipidus?
Manage underlying cause e.g stop lithium
Mild cases can be managed conservatively
Cranial DI - desmopressin (to replace ADH not being made by hypothalamus)
Nephrogenic DI - high dose desmopressin
