Diabetes Insipidus

Question 1

Define:

Answer 1

Inadequate secretion or insensitivity to vasopressin (ADH) leading to passage of large volumes (>3L/day) of dilute urine

Question 2

Aetiology/risk factors:

Answer 2

Cranial - do not produce ADH

Nephrogenic - insensitivity of collecting duct to ADH

Question 3

Causes of cranial:

Answer 3

• Idiopathic (50%)
• Congenital: defects in ADH gene, DIDMOAD
• Tumours (e.g. pituitary tumour, craniopharyngioma, metastases)
• Infiltrative (e.g. sarcoidosis)
• Infection (e.g. meningitis)
• Vascular (e.g. aneurysms, Sheehan syndrome)
• Trauma (e.g. head injury, neurosurgery)
• Hypophysectomy
• Autoimmune hypophysitis

Question 4

Causes of nephrogenic:

Answer 4

• Idiopathic
• Inherited
• Metabolic: low potassium, high calcium
• Drugs (e.g. lithium)
• Post-obstructive uropathy
• Pyelonephritis
• Chronic renal disease
• Pregnancy
• Osmotic diuresis (e.g. diabetes mellitus)
• Amyloidosis
• PKD
• Hypercalciuria
• Lithium toxicity

Question 5

Epidemiology:

Answer 5

• Median onset is 24 yrs

* Depends on cause

Question 6

Symptoms:

Answer 6

Polyuria
Polydipsia
Nocturia

In children:

• Enuresis (bed wetting)
• Sleep deprevation

Question 7

Signs:

Answer 7

Can show signs of dehydration (postural hypotension, dry mucous membranes, tachycardia and reduced tissue tugor)

If cranial and maintain adequate fluid intake then few signs

Urine output greater than 3 litres a day

Signs related to the cause such as bitemporal hemianopia (pituitary adenoma)

Question 8

Investigations:

Answer 8

Water deprivation test for 8 hrs.

• monitor weight as if lose >3% the stop
• Psychogenic will show normal concentrated urine
• In central will concentrate after desmopressin
• Nephrogenic will not

Bloods: U + E’s, Ca2+

Plasma osmolality (increased)

Urine osmolality (reduced)

Question 9

Management of cranial:

Answer 9

• Treat the CAUSE
o Find cause: MRI head
o Give desmopressin (vasopressin analogue – V2 receptor specific)
o If mild - chlorpropamide or carbamazepine can be used to potentiate the residual effects of any residual vasopressin

Question 10

management of nephrogenic:

Answer 10

o Thiazide diuretics e.g. bendroflumethiazide – inhibits Na/Cl transporter in DCT causing diuretic effect, which causes compensatory increase in Na reabsorption from PCT
o NSAIDs lower urine volume and plasma Na by inhibiting prostaglandin synthesis.

Question 11

Complications:

Answer 11

• Hypernatraemic dehydration

* Excess desmopressin –> hyponatraemia

Question 12

Prognosis:

Answer 12

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