Diabetes Insipidus

Question 1

Define diabetes insipidus

Answer 1

Metabolic disorder characterised by the inadequate secretion of or insensitivity to vasopressin leading to hypotonic polyuria

Question 2

Aetiology of cranial diabetes insipidus

Answer 2

Cranial: 
Pituitary tumour
Sarcoidosis
Meningitis
Aneurysms
Sheehan's
Head injury
SAH
Phenytoin

Question 3

Define nephrogenic diabetes insipidus

Answer 3

Lithium
Uropathy 
Pyelonephritis
Osmotic diuresis e.g. DM
Pregnancy
Wolfram syndrome

Question 4

What is Wolfram syndrome

Answer 4

DM, optic atrophy (DI, sensorineural deafness)

Question 5

General aetiology of diabetes insipidus

Answer 5

Aquaporins fail to activate and the luminal membrane of the collecting duct remains impermeable, resulting in large volume hypotonic urine and polydipsia

Question 6

Risk factors for diabetes insipidus

Answer 6

Pituitary surgery or stalk lesions
Craniopharyngioma
Traumatic brain injury 
Medication
Autoimmune disease
Family history

Question 7

Symptoms of diabetes insipidus

Answer 7

Polyuria (3L-20L)
Polydipsia
Nocturia
Skin rashes (papular rashes, ulcers, erythema nodosum)

Question 8

Signs of diabetes insipidus

Answer 8

volume depletion: dry mucous membranes, poor skin turgor, tachycardia, hypotension

Hypernatraemia: irritability, restlessness, lethargy, spasticity, hyper-reflexia

Visual field defects or focal motor defects

Sensorineural deafness (Wolfram syndrome)

Skin lesions e.g. papular rashes or ulcers (Langerhans’ cell histiocytosis)

Erythema nodosum (sarcoidosis)

Question 9

Investigations for diabetes insipidus

Answer 9

Urine osmolality and dipstick: reduced, negative (exclude DM)

24h urine collection: >3L per 24 hours

Water deprivation test: osmolality <300, serum >290

Desmopressin stimulation test: distinguish between central and nephrogenic

Bloods: osmolality, glucose, U&Es

Question 10

Management for central diabetes insipidus

Answer 10

Correct hypernatraemia using hypotonic oral/IV fluids

1. Desmopressin 0.1-1mg/day oral
2. Oral/IV fluids (5% dextrose 0.45% sodium chloride)

Question 11

Management for nephrogenic diabetes insipidus

Answer 11

Correct hypernatraemia uring hypotonic oral/IV fluids

1. Maintenance of adequate fluid intake
2. Treat underlying cause
3. Consider hydrochlorothiazide

Question 12

Complications of diabetes insipidus

Answer 12

Hypernatraemia
Thrombosis
Bladder and renal dysfunction
Iatrogenic hyponatraemia

Question 13

Prognosis of diabetes insipidus

Answer 13

Depends on the aetiology and co-morbs

Generally good