Diabetes insipidus Flashcards
What is diabetes insipidus?
Deficiency of vasopressin (ADH) or insensitivity at the kidneys
What are causes of cranial diabetes insipidus?
- Idiopathic
- Congenital - DIDMOAD
- Tumour - craniopharyngioma, mets, pituitary tumour
- Trauma
- Autoimmune hypophysitis
- Infiltration - histiocytosis, sarcoidosis
- Vascular - haemorrhage
What are nephrogenic causes of diabetes insipidus?
- Inherited
- Metabolic - hypokalaemia, hypercalcaemia
- Drugs - lithium
- CKD/Renal tubular acidosis
- Post-obstructive uropathy
What are features of diabetes insipidus?
- Polyuria
- Polydipsia
- Dehydration
- Symptoms of hypernatraemia
- Symptoms of hypokalaemia
How much fluid will individuals with diabetes insipidus produce per day?
10-15L
What investigations would you do if you suspected diabetes insipidus?
- Bedside - urine dipstick, cap glucose
- Bloods - U+E’s, Glucose, Ca2+, serum osmolality
- Imaging - MRI - cranial cause
- Other - Urine:plasma osmolality, Water Deprivation test
What is involved in the water deprivation test used to diagnose diabetes insipidus?
- Fasting and no fluids from 07:30 hours
- Monitor serum and urine osmolality, urine volume and weight hourly for up to 8 hours.
- Abandon fluid deprivation if weight loss >3% occurs.
- If serum osmolality >300 mOsm/kg and/or urine osmolality <600 mOsm/kg give desmopressin 2 µg i.m. at end of test - this is used to distinguish cranial from nephrogenic DI
What might you find on water deprivation test in someone with DI?
Serum osmolality rises above normal without adequate concentration of urine osmolality (i.e. serum osmolality >300 mOsm/kg; urine osmolality <600 mOsm/kg).
How would you manage someone with diabetes insipidus?
- Treat the cause - usually sorts out nephrogenic DI
- Desmopressin - Cranial DI
What urine:plasma osmolality is indicative of Diabetes insipidus?
<2 is indicative of DI
What might you find on investigation of U+Es in someone with DI?
- Hypernatraemia
- Hypokalaemia
On water deprivation testing, what would indicate primary polydipsia as a cause of polyuria?
Urine concentrates, but less than normal, e.g. >400-600mOsmol/kg.
On water deprivation testing, what would indicate cranial DI as a cause of polyuria?
Response to desmopressin - Urine osmolality increases to >600mOsmol/kg after desmopressin (if equivocal an extended water deprivation test may be tried – no drinking from 18:00 the night before).
On water deprivation testing, what would indicate nephrogenic DI as a cause of polyuria?
No increase in urine osmolality after desmopressin - remains low
