central diabetes insipidus Flashcards
definition
inadequate secretion of anti-diuretic hormone from the hypothalamus which causes excessive urination (polyuria) and excessive thirst (polydipsia)
causes
- most commonly is idiopathic
- trauma: RTAS, iatrogenic
- wolframs syndrome (DIDMOAD) which is inherited
investigations
- water deprivation test
- baseline serum to urine osmolality
in diabetes insidious what happens to the osmolality
the serum osmolality increases and the urine osmolality decreases
water deprivation test
at 8am patient empties the bladder, volume of urine is recorded and serum and urine osmolality and patient wight measured
from this point onwards
the patient is fluid restricted and the values are remeasured every hour
the test can be stopped if at any point
- the urine osmolality increases above 600 or the serum osmolality falls below 295 as this is normal and rules OUT diabetes insidious
- the urine osmolality falls below 600 or the serum osmolality increases above 300 as this confirms DIABETES INSIPIDUS
diabetes insipididus is confirmed then wha
administer DDAVP (demopressin) which allows you to distinguish between central diabetes insidious or nephrogenic diabetes insidious
if its central diabetes insidious
- after administration of desmopressin the urine osmolality should start to increase by 50% and the serum osmolality should fall
in nephrogenic diabetes insipidus
there is no response to the desmopressin and urine osmolality remains unchanged as the problem is a resistance to anti-diuretic hormone not that there isn’t enough being secreted by the hypothalamus like in central diabetes ionsipidus
management of central diabetes insidious
desmospray (nasally): 10-60mcg a day
OR
desmopressin oral tablets: 100-1000mcg a day
OR
desmopressin injections: post surgery or in an emergency
