Diabetes Insipidus Flashcards
What is Diabetes Insipidus? (2 things)
- Lack of ADH secretion
OR
- Reduced sensitivity to ADH by kidney
What does DI cause?
Passing beh dilute urine
What are the 2 types of DI?
- Nephrogenic
- Cranial
What is Nephrogenic DI?
When CD of kidney X respond to ADH
What are the causes of Nephrogenic DI? (5 things)
- Inherited
- Electrolye abn (low K / high Ca)
- Drugs (e.g lithium.. used in bipolar)
- Chronic renal disease
- Post-obst uropathy
What is Cranial DI?
Hypothalamus does’t produce ADH for pit to secrete
What are the causes of Cranial DI? (6 things)
- Idiopathic (50%)
- Brain tumour (may present w DI + hypopituitarism)
- Brain surgery
- Trauma
- Haemorrhage
- Infections (e.g meningitis / TB)
What are the CF of DI? (5 things)
- Polyuria
- Polydipsia
- Dehydration
- Postural hypotension
- Hypernatraemia symptoms (thirst + lethargy)
What investigations should you do for sus DI? (6 things)
- Water deprivation test (aka desmopressin stimulation test) (GOLD)
- Serum osmolality (high)
- Urine osmolality (low)
- UnE (low K causes Nephrogenic DI)
- Calcium (high Ca causes Nephrogenic DI)
- Glucose (to exclude DM)
What is a differential diagnosis that presents similarly to DI?
Primary Polydipsia
- Pt has normal ADH system but dey jus drink behh water
- Cause unknown but assoc w schizophrenia / mania
Which investigation for sus DI will differentiate DI from Primary Polydipsia?
Water deprivation test (aka Desmopressin stimulation test)
It will also tell you the type of DI if they have it (Nephrogenic / Cranial)
What is the method of the Water deprivation test? (4 steps)
- No fluids for 8 hours
- Measure Urine osmolality
- Desmopressin (synthetic ADH) given (dey can drink now too)
- Measure Urine osmolality again after 8 hours
What are the results of Water deprivation test to differentiate between DI and Primary Polydipsia?
LOW urine osmolality @ 8 hrs deprivation: DI
HIGH urine osmolality @ 8 hrs deprivation: Primary Polydipsia
What are the results of Water deprivation test to differentiate between Nephrogenic n Cranial DI?
LOW urine osmolality after synthetic ADH given: Nephrogenic
HIGH urine osmolality after synthetic ADH given: Cranial
What is the explanation of the Water deprivation test for Nephrogenic DI? (3 things)
- Patient kidneys X respond to ADH anyways
- They will always jus dilute their urine
- So urine osmolality stays LOW even after synthetic ADH given
What is the explanation of the Water deprivation test for Cranial DI? (2 things)
- Patient can respond to ADH, they jus can’t make any
- When synthetic ADH given, they respond by reabs water + concentrating urine –> HIGH urine osmolality
