Diabetes Insipidus

Question 1

Define diabetes insipidus

Answer 1

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

Question 2

Aetiology of diabetes insipidus

Answer 2

Cranial/central: Failure of ADH secretion by the posterior pituitary
- Idiopathic
- Tumours e.g. pituitary tumour
- Infiltrative e.g. sarcoidosis
- Vascular e.g. aneurysms, Sheehan syndrome
- Infection e.g. meningitis
- Trauma e.g. head injury, neurosurgery, SAH
- Autoimmune e.g. Langerhan’s cell histiocytosis, sarcoid, IgG4, Hypophysitis (SE of checkpoint inhibitors)
- Iatrogenic e.g. phenytoin, transphenoidal surgery
- Neoplasia e.g. craniopharyngioma
- Congenital e.g. pituitary stalk insufficiency syndrome

Nephrogenic: Insensitivity of the collecting duct to ADH
- Idiopathic
- Drugs e.g. lithium, diuretics
- Post-obstructive uropathy
- Pyelonephritis
- Pregnancy
- smotic diuresis e.g. DM
- Primary hyperparathyroidism

Question 3

Symptoms of diabetes insipidus

Answer 3

Polyuria
Polydipsia
Nocturia
Skin rashes
- Papular/ulcers (langerhan’s cell histiocytosis)
- Erythema nodosum (sarcoidosis)
irritability, restlessness, lethargy, spasticity (hypernatraemia)

Question 4

Signs of diabetes insipidus on examination

Answer 4

General: Volume deplete: Dry mucous membranes, poor skin turgor, sunken eyes, poor CRT | skin lesions (Langerhan’s cell histiocytosis)
Obs: hypotension and tachycardia
CN: visual field defects (?pituitary mass), sensorineural deafness
Neuro: spasticity, hyperreflexia (hyperNa), focal motor deficits (intracranial path)

Question 5

Investigations for diabetes insipidus

Answer 5

Urine dip: exclude DM
Urine Osm: LOW <300
24h urine collection: >3L/24h

Osmolality: High
Glucose: exclude DM
U&Es: hypernatraemia, hypokalaemia (N-DI), urea nitrogen elevated (volume depletion or renal disease)
Bone profile: hypercalcaemia (N-DI)

WATER DEPRIVATION TEST

Question 6

How do you interpret a water deprivation test

Answer 6

Normal result: [0h] normal pOsm [8h] uOsm high >600 [DDAVP] remains high

Psychogenic: [0h] pOsm low [8h] uOsm high >400 [DDAVP] remains high >400

Cranial DI: [0h] pOsm high [8h] uOsm low <300 [DDAVP] uOsm increases >600

Nephrogenic DI: [0h] high pOsm [8h] uOsm low <300 [DDAVP] Remains low <300

Question 7

What is the management for central diabetes insipidus

Answer 7

1. Desmopressin 0.1-1mg/day orally given in 2-3 divided doses
   a. Spray at night and see how long it lasts
   b. Oral tabs/melts
   c. Drink to thirst
2. Oral/IV fluids
   a. IV 5% dextrose and 0.45% sodium chloride
   Encourage to drink

Question 8

Management for nephrogenic DI

Answer 8

1. Maintenance of adequate fluid intake: Low solute diet
2. Treatment of underlying cause
3. Thiazide diuretics
   - Consider hydrochlorothiazide 12.5-50mg orally once

Question 9

Complications of diabetes inspidus

Answer 9

Hypernatraemia (Correct the serum sodium via oral/IV fluids)
Thrombosis
Bladder and renal dysfunction
Iatrogenic hyponatraemia

Question 10

Prognosis for diabetes insipidus

Answer 10

Outcome and outlook depend on the underlying aetiology, type of DI and associated comorbidities
Cranial DI following surgery or brain injury may be transient
Nephrogenic DI secondary to hypercalcaemia or hypokalaemia commonly resolves following correction
Majority of central DI are controlled on synthetic long acting desmopressin/DDAVP
Patients with large-volume polyuria will need regular renal or bladder imaging, to avoid occult bladder or renal tract abnormalities such as hydronephrosis and bladder dysfunction