Diabetes Insipidus Flashcards
Define:
Inadequate secretion or insensitivity to vasopressin (ADH) leading to passage of large volumes (>3L/day) of dilute urine
Aetiology/risk factors:
Cranial - do not produce ADH
Nephrogenic - insensitivity of collecting duct to ADH
Causes of cranial:
- 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
Causes of nephrogenic:
- 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
Epidemiology:
- Median onset is 24 yrs
* Depends on cause
Symptoms:
Polyuria
Polydipsia
Nocturia
In children:
- Enuresis (bed wetting)
- Sleep deprevation
Signs:
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)
Investigations:
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)
Management of cranial:
• 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
management of nephrogenic:
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.
Complications:
- Hypernatraemic dehydration
* Excess desmopressin –> hyponatraemia
Prognosis:
- 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)