Diabetes insipidus Flashcards
Why does cranial diabetes insipidus occur?
The hypothalamus does not produce ADH for the pituitary gland to secrete
Why does nephrogenic diabetes insipidus occur?
The collecting ducts of the kidneys do not respond to antidiuretic hormone
Where is antidiuretic hormone produced?
The hypothalamus
Where is antidiuretic hormone secreted from?
The posterior pituitary gland
What does antidiuretic hormone do?
Stimulates water reabsorption from the collecting ducts in the kidneys
What two presentations are typical of diabetes insipidus due to the kidneys being unable to reabsorb water and concentrate the urine?
Polyuria - excessive urination
Polydipsia - excessive thirst
Give some causes of nephrogenic diabetes insipidus?
Idiopathic
Medications
Hypercalcaemia
Hypokalaemia
Kidney diseases
Genetic mutation of ADH receptor gene
Give some causes of cranial diabetes insipidus?
Idiopathic
Brain injury / tumour / surgery
Brain infections
Genetic mutations in the ADH gene
Wolfram syndrome
What are the presenting features of diabetes insipidus?
Polyuria
Polydipsia
Dehydration
Postural hypotension
What test is used to diagnose diabetes insipidus?
Water deprivation test
What will be shown on investigation is diabetes insipidus is present?
Low urine osmolality
High / normal serum osmolality
More than 3 litres on a 24-hour urine collection
How is the water depravation test carried out?
Patient avoids fluids for up to 8 hours before the test
Urine osmolality is measured
If urine osmolality is low: the patient is given desmopressin
The urine osmolality is then measured over the 2-4 hours following desmopressin
What is primary polydipsia?
A patient with a normally functioning ADH system that drinks excessive amounts of water causing excessive urine production
What will water depravation cause in the urine osmolality of a patient with primary polydipsia?
Urine osmolality will be high
What result of a water depravation test rules out diabetes insipidus as a potential diagnosis?
A high urine osmolality
If urine osmolality is high after desmopressin what is the likely diagnosis?
Cranial diabetes insipidus
If urine osmolality is low after desmopressin what is the likely diagnosis?
Nephrogenic diabetes insipidus
Why is urine osmolality results always low in nephrogenic diabetes insipidus?
The patient is unable to respond to antidiuretic hormone
What is desmopressin?
Synthetic antidiuretic hormone (ADH)
How is cranial diabetes insipidus managed?
Desmopressin - replaces absent antidiuretic hormone
What should be monitored if desmopressin has been prescribed?
Serum sodium
Desmopressin presents a risk of hyponatraemia
How can nephrogenic diabetes insipidus be managed?
Ensuring access to plenty of water
High-dose desmopressin
Thiazide diuretics
NSAIDs
