Diabetes Insipidus Flashcards

1
Q

Define:

A

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

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2
Q

Aetiology/risk factors:

A

Cranial - do not produce ADH

Nephrogenic - insensitivity of collecting duct to ADH

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3
Q

Causes of cranial:

A
  • 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
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4
Q

Causes of nephrogenic:

A
  • 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
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5
Q

Epidemiology:

A
  • Median onset is 24 yrs

* Depends on cause

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6
Q

Symptoms:

A

Polyuria
Polydipsia
Nocturia

In children:

  • Enuresis (bed wetting)
  • Sleep deprevation
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7
Q

Signs:

A

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)

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8
Q

Investigations:

A

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)

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9
Q

Management of cranial:

A

• 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

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10
Q

management of nephrogenic:

A

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.

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11
Q

Complications:

A
  • Hypernatraemic dehydration

* Excess desmopressin –> hyponatraemia

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12
Q

Prognosis:

A
  • 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)
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