Diabetes insipidus

Question 1

What are the 2 types of DI and explain them?

Answer 1

Cranial DI - deficiency of ADH

Nephrogenic DI - insensitivity to ADH

Question 2

Name 4 causes of cranial DI

Answer 2

Idiopathic
Post-head injury 
Pituitary surgery 
Craniopharyngioma 
Haemochromatosis

Question 3

Name 4 causes of nephrogenic DI

Answer 3

Genetic
Electrolytes: hyperCa, hypoK
Drugs: lithium
Tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis

Question 4

What are the sx?

Answer 4

Polyuria

Polydipsia

Question 5

How can it be differentiated from DM?

Answer 5

No glycosuria

Question 6

What Ix are done?

Answer 6

Measure urine vol. >3L/day

Plasma/ urine osmolality

• high plasma osmolality
• low urine osmolality

Water deprivation test
(IM desmopressin)
- Cranial: urine osmolality >600mOsmol/kg
- Nephrogenic: no increase in urine osmolality

Question 7

How is cranial DI Ix?

Answer 7

MRI pituitary

Question 8

How is cranial DI mx?

Answer 8

Oral desmopressin

Question 9

How is nephrogenic DI mx?

Answer 9

Treat cause
Bendroflumethiazide
NSAIDs

Question 10

How is DI mx acutely?

Answer 10

Do urgent plasma U&E, serum and urine osmolalities

Monitor urine output
Check U&E BD

IV fluid to keep up with urine output
Desmopressin 2ug IM

Question 11

What is osmolality?

Answer 11

Concentration of solution expressed as total no. of solute particles per kg