Diabetes insipidus

Question 1

sx triad diabetes insipidus

Answer 1

polyuria (>3L)
nocturia
polydipsia

Question 2

what ix findings strongly suggest DI

Answer 2

• hypernatraemia (apparent hypernat due to decreased H2O in blood)
• decreased urine osmolality
• increased serum osmolality

Question 3

DI caused by

Answer 3

hyposecretion or insensitivity to ADH

Question 4

causes of cranial DI

Answer 4

idiopathic
tumour
intracranial surgery
head injury
infection
vascular (haemorrhage, sheehan)

Question 5

causes of nephrogenic DI

Answer 5

idiopathic
hypokal
hyperkal
CKD
orlistat, lithium
pregnancy
can be congenital or inherited

Question 6

low osmolality = dilute or conc?

Answer 6

dilute

Question 7

Ix?

Answer 7

24h urinary collection to confirm polyuria
-serum glucose to exclude DM
-U+Es
-simultaneous plasma and urine omolality
fluid deprivation test with response to desmopressin
-many need MRI head

Question 8

what is water deprivation test

Answer 8

fluids withheld over 8h.

if no change in water loss despite deprivatino, give desmopressin to distinguish between cranial and nephrogenic

Question 9

interpretation of water deprivation test?

Answer 9

-serum osmolality rises above normal (more conc) without adequate incfrease in urine osmolality (urine still dilute)

nephrogenic DI: desmopressin does not conc urine
cranial DI: urine osmolality rises by >50% after desmopressin

Question 10

treatment of DI

Answer 10

desmopressin (synthetic vasopressin)

treat underlying cuase