Diabetes Insipidus Flashcards
What are the 2 types of DI?
Cranial DI
Nephrogenic DI
What is cranial DI?
Decreased secretion of antidiuretic hormone (ADH) from the pituitary
What is cranial DI due to?
Hypothalamus doesn’t produce enough ADH for pituitary to secrete
What is nephrogenic DI?
Decreased sensitivity of collecting ducts to antidiuretic hormone
What are the causes of cranial DI?
- Brain tumours (craniopharyngiomas)
- Head injury
- Brain malformations
- Brain infections (meningitis)
- Brain surgery or radiotherapy
- Hemochromatosis
- Sarcoidosis
What brain infections can cause cranial DI?
Meningitis
Encephalitis
Tuberculosis
What are the causes of nephrogenic DI?
- Mutation on AVPR2 gene on chromosome x
- Lithium
- Intrinsic kidney disease
- Electrolytes- Hypercalcaemia and hypokalaemia
How can lithium cause nephrogenic DI?
Desensitises kidneys ability to respond to ADH
What intrinsic kidney disease can cause nephrogenic DI?
Obstruction
Pyelonephritis
Sickle cell anaemia
How does DI present?
- Polyuria- lots of dilute urine
- Polydipsia- extreme thirst
- Hypernatremia
- Nocturia
- Postural hypotension
How id DI diagnosed?
Water deprivation test
What is the water deprivation test?
Give synthetic ADH
Measure urine osmolarity 8 hours later
What are the results of a cranial DI water deprivation test?
Low ADH before
High urine osmolarity
What are the results of a nephrogenic DI water deprivation test?
Low ADH
Low urine osmolarity (failure to respond)
What are the results of polydipsia water deprivation test?
High ADH
High urine osmolarity
