Diabetes Insipidus

Question 1

What are the symptoms of Diabetes Insipidus?

Answer 1

Polydipsia
Polyuria
Dehydration
Hypernatraemia (Lethargy, thirst, confusion, coma)

Question 2

What are the cranial causes of Diabetes Insipidus?

Answer 2

Idiopathic
Congenital
Tumours
Trauma
Haemorrhage
Infection
Infiltration (Sarcoidosis)

Question 3

Define Diabetes Insipidus

Answer 3

A lack of production of ADH or the kidney not responding to ADH. (Cranial or Nephrogenic Diabetes Insipidus)

Question 4

What are the nephrogenic causes of Diabetes Insipidus?

Answer 4

Congenital
Metabolic; ↓K, ↑Ca
Iatrogenic; Lithium
Post obstructive uropathy (Urine cannot drain so backs up into kidney causing hydronephrosis)

Question 5

What investigations can be done in a patient with suspected Diabetes Insipidus?

Answer 5

Bloods - U+Es, Ca2+, Glucose
Urine + Plasma osmolality - if U:P osmolality ratio >2 - exclude DI 
MRI
Water suppression test
Desmopressin (synthetic ADH) trial

Question 6

What is the water suppression test for DI?

Answer 6

Patient not given any fluids, if has DI they will continue to produce large volumes of dilute fluid
ADH blood test taken too to assess levels

Question 7

What is the desmopressin trial for DI?

Answer 7

Patient given synthetic ADH;
Decreased urine production - shows not enough ADH = cranial causes
Continued excess urine production - shows enough ADH, kidneys not responding = Nephrogenic causes

Question 8

What are the differentials for DI?

Answer 8

DM
Diuretics
Lithium
Psychogenic/Primary polydipsia (excessive fluid intake due to feeling of dry mouth)

Question 9

How do you manage a patient with cranial DI?

Answer 9

Find cause

Desmopressin (synthetic ADH)

Question 10

How do you manage a patient with Nephrogenic DI?

Answer 10

Treat the cause