Cranial Diabetes Insipidus

Question 1

what causes it?

Answer 1

familial - very rare

• isolated in most cases
• DIDMOAD (DI, DM, optic atrophy, deaf)

acquired

• idiopathic in 50%
• trauma; road accidents, surgery, skull fracture
• tumour; sarcoid, ext irradiation, meningitis

Question 2

how is it diagnosed?

Answer 2

by the water deprivation test (NO water or 8-12 hrs)
check serum and urine osmolalities for 8hr and then 4 hr after giving IM DDAVP
if ur/serum osmol ratio>2 then it is normal, otherwise DI
if low and it improves after DDAVP then it is due to ‘cranial DI’ i.e. deficiency of DDAVP (anf not nephrogenic DI)

Question 3

how is it treated?

Answer 3

desmospray - nasally 10-60mcg/day
desmopressin oral tablets - 100-1000mcg per day
desmopressin injection - 1-2mcg IM per day e.g. emergency or post pituitary surgery