Diabetes Insipidus Flashcards
What is diabetes insipidus?
An inability of the body to concentrate urine
It is caused by a lack of ADH, or a lack of response to ADH
What is cranial diabetes insipidus?
Where there is insufficient vasopressin release from the hypothalamo-pituitary axis
What is nephrogenic diabetes insipidus?
Where the collecting ducts of the kidneys do not respond to ADH
What are the causes of cranial diabetes insipidus?
Brain tumours
Brain injury
Brain surgery
Brain infections
Genetic mutations in ADH gene
Wolfram syndrome
What are the causes of nephrogenic diabetes insipidus?
Medications - lithium
Genetic mutations in the ADH receptor gene
Hypercalcaemia
Hypokalaemia
Kidney diseases e.g PCKD
What is primary polydipsia?
Excessive intake of fluid, that leads to reduced serum osmolality, and the suppression of ADH
This causes polyuria
What are the clinical features of diabetes insipidus?
Polyuria
Nocturia
Polydipsia
Fatigue
Dry mucous membranes
Reduced skin turgor
Tachycardia
Hypotension /postural hypotension
Hypernatraemia
What are the primary investigations used in the diagnosis of diabetes insipidus?
Urine and serum osmolality
- High serum osmolality
- Low urine osmolality
U&Es
- Sodium may be raised
- Deranged potassium and calcium may suggest nephrogenic DI
Serum glucose
- Exclude diabetes
24 hour urine output
Water deprivation test
What is a water deprivation test?
The patient is deprived of water for 8 hours
- Serum and urine osmolality are measured hourly
What is a positive water deprivation test?
Water deprivation causes low urine osmolality and high serum osmolality
What test differentiates between cranial and nephrogenic DI?
Desmopressin suppression test
How does the desmopressin suppression test differentiate between cranial and nephrogenic diabetes insipidus?
After desmopressin:
- Urine osmolality remains low in nephrogenic DI, as the body still cannot respond to ADH
- Urine osmolality is high in cranial DI, as the body is able to respond to ADH
What is the management of cranial DI?
Desmopressin
Monitor serum sodium
Manage fluid balance
What is the management of nephrogenic diabetes insipidus?
Manage fluid balance
Treat underlying cause
Sodium restriction
Thiazide diuretics - can reduce urine output in nephrogenic DI
