Diabetes Insipidus

Question 1

Define Diabetes Insipidus?

Answer 1

A disorder of inadequeate secretion or of insensitivity to vasopressin (ADH) leading to hypotonic polyuria

Question 2

What is the aetiology of Central Diabetes Insipidus?

Answer 2

Failure of ADH secretion by the posterior pituitary

Question 3

What is the aetiology of Nephrogenic Diabetes Insipidus?

Answer 3

Insensitivity of the collecting duct to ADH

Water channels fail to activate and the luminal membrane of the collecting duct remains impermeable to water

Question 4

What does Diabetes Insipidus result in?

Answer 4

Large volumes of hypotonic urine and polydipsia

Question 5

What are the causes of Central Diabetes Insipidus?

Answer 5

Idiopathic
Tumours (e.g. Pituitary Tumours)
Infiltrative (e.g. sarcoidosis)
Infection (e.g. meningitis)
Vascular (e.g. aneurysms, Sheehan Syndrome)
Trauma (e.g. head injury, neurosurgery)

Question 6

What are the causes of Nephrogenic Diabetes Insipidus?

Answer 6

Idiopathic 
Drugs (e.g. Lithium)
Post-obstructive uropathy
Pyelonephritis 
Pregnancy
Osmotic diuresis (e.g. Diabetes Mellitus)

Question 7

What is the epidemiology of Diabetes Insipidus?

Answer 7

Median onset is 24 yrs

Depends on cause

Question 8

What are the presenting symptoms of Diabetes Insipidus?

Answer 8

Polyuria
Nocturia
Polydipsia
Other symptoms depend on aetiology

Question 9

What are the symptoms of Diabetes Insipidus in children?

Answer 9

Enuresis (bed-wetting)

Sleep disturbance

Question 10

What are the signs of Diabetes Insipidus on physical examination?

Answer 10

Central Diabetes Insipidus has few signs if the patient drinks sufficiency to maintain adequate fluid levels
Urine output > 3 L/day
If fluid intake < fluid output signs of dehydration will be present
Signs related to the cause (e.g. visual defect due to pituitary tumour)

Question 11

What are some common signs of dehydration?

Answer 11

Tachycardia
Reduced Tissue Turgor
Postural Hypotension
Dry Mucous Membranes

Question 12

What bloods would you do for Diabetes Insipidus and why?

Answer 12

U&Es and Ca2+
Increased plasma Osmolality
Decreased urine osmolality

Question 13

What is the water deprivation test?

Answer 13

Used to investigate Diabetes Insipidus

Question 14

What occurs in the Water Deprivation Test?

Answer 14

Water is restricted for 8 hrs
Plasma and urine osmolality are measured every hour for 8 hrs
Weight the patient hourly to monitor level of dehydration
Stop the test if the fall in body weight is > 3%v
Desmopressin is given after 8 hrs and urine osmolality is measured

Question 15

What are the results in a normal person for a Water Deprivation Test?

Answer 15

Water Restriction causes:

• Increased Plasma Osmolality
• Increased ADH secretion
• Increased water reabsorption
• Increase in urine osmolality (urine > 600 mosmol/kg)

Question 16

What are the results in a person with Diabetes Insipidus for the Water Deprivation Test?

Answer 16

Lack of ADH activity means that urine can’t be concentrated
Urine osmolality is low (< 400 mosmol/kg)
Cranial - urine osmolality rises > 50% following administration of desmopressin
Nephrogenic - urine osmolality rises by < 45% following administration of desmopressin

Question 17

What is the general management plan for Diabetes Insipidus?

Answer 17

Treat the cause

Question 18

What is the management plan for Cranial Diabetes Insipidus?

Answer 18

Give desmopressin (vasopressin analogue)
If mild - chloropropramide or carbamazepine can be used to potentiate the residual effects of any residual vasopressin

Question 19

What is the management plan for Nephrogenic Diabetes Insipidus?

Answer 19

Sodium and/or protein restriction helps with polyuria

Thiazide diuretics

Question 20

What are the possible complications of Diabetes Insipidus?

Answer 20

Hypernatraemic dehydration

Excess Desmopressin leads to hyponatraemia

Question 21

What is the prognosis for patients with Diabetes Insipidus?

Answer 21

Depends on cause
Cranial Diabetes Insipidus may be transient following head trauma
It may be cured by removing the cause (e.g. drug discontinuation, tumour resection)