Neurohypophysial disorders

Question 1

In a water deprivation test, what would you expect to happen to the osmolality of urine

Answer 1

You would expect the osmolality of urine to increase.

Question 2

What is DDVAP

Answer 2

A modified form of Vasopressin- usually given as a nasal spray

Question 3

What does the osmolality of the patient’s urine rises after the administration of DDAVP

Answer 3

Vasopressin binds to V2 receptors on the renal collecting duct cells of the kidney. Increased water reabsorption- less water in urine- more concentrated urine- plasma osmolality increases.

Question 4

Considering the fact that the patient responds to vasopressin, what does this mean in terms of what causes the diabetes insipidus

Answer 4

Unlikely to be nephrogenic or renal- as Kidney is not resistant to Vasopressin.
Likely to be cranial- damages to pituitary gland- tumour, autoimmune disease, trauma, inflammation

Question 5

Describe the water deprivation test

Answer 5

Can’t drink water for 12 hours before the test- should be dehydrated in the plamsa

Question 6

What additional tests should be carried out

Answer 6

MRI of the pituitary gland with contrast of brain- bright spot on MRI normal. Could show a tumour.