Endocrine - Diabetes Insipidus Flashcards
Why does diabetes insipidus occur?
Lack of ADH (cranial diabetes insipidus)
Lack of response to ADH (nephrogenic diabetes insipidus)
Where is ADH produced?
Hypothalamus
Secreted by posterior pituitary
What is primary polydipsia?
Patient has normally functioning ADH
Drinks excessive water causing polyuria
What can cause nephrogenic diabetes insipidus?
Idiopathic
Medications - Lithium for bipolar disease
Hypercalcaemia
Hypokalaemia
Kidney disease (polycystic kidney disease)
What causes cranial diabetes insipidus?
Brain tumours
Brain injury
Brain surgery
Brain infections (meningitis or encephalitis)
Genetic mutations in ADH gene (autosomal dominant)
Wolfram syndrome
How does diabetes insipidus present?
Polyuria
Polydipsia
Dehydration
Postural hypotension
What investigations are used for diabetes insipidus?
Low urine osmolality (lots of water diluting urine)
High/normal serum osmolality (increased water intake)
More than 3 litres of urine
What is the test of choice for diagnosing diabetes insipidus?
Water deprivation test
Patient avoids fluids for 8 hours
If urine osmolality is low synthetic ADH is given, then measured again over next 2-4 hours
High urine osmolality after water depivation rules out diabetes insipidus
In cranial diabetes the kidneys can still respond to ADH, after getting ADH the urine osmolality is high
In nephrogenic it is low before and after as the kidneys cannot respond to ADH
How is diabetes insipidus managed?
Underlying cause treated e.g. stopping lithium
Cranial diabetes insipidus desmopressin can be used to replace ADH
Serum sodium must be measured as hyponatraemia risk
Nephrogenic diabetes insipidus
- Ensure high water access
- High-dose desmopressin
- Thiazide diuretics
- NSAIDs
