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Endocrinology > Diabetes Insipidus > Flashcards

Diabetes Insipidus Flashcards

1
Q

Give the definition

A

Passage of large volumes (>3L/day) of dilute urine due to impaired water reabsorption in the kidney

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2
Q

What are the possible mechanisms by which DI occurs

A
  1. Reduced ADH secretion from the posterior pituitary - CRANIAL DI
  2. Impaired response of the kidney to ADH - NEPHROGENIC DI
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3
Q

What are the causes of cranial DI

A
  • Idiopathic (50%)
  • Congenital: defects in ADH gene, DIDMOAD
  • Trauma - head injury, surgery
  • Tumour - craniopharyngioma
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4
Q

What are causes of nephrogenic DI?

A
  • Genetic
  • Metabolic - hypercalcaemia, hypokalaemia
  • Drugs - lithium, demeclocycline
  • CKD
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5
Q

What are the features of DI?

A

Polyuria
Polydipsia
Dehydration
Hypernatraemia sx (weakness, nausea, confusion, muscle twitching)

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6
Q

What investigations would you do?

A
  1. Urine osmolality - low (<300mmol/kg)
  2. Serum sodium - elevated
  3. Ca2+, K+
  4. Urine dipstick - exclude DM
  5. Serum glucose
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7
Q

What test is diagnostic? what result is positive for DI?

A

Water deprivation test
Deprived of fluids for 8 hrs
+ve: insufficient rise in urine osmolality i.e. unable to conc urine

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8
Q

Why does hypernatraemia occur?

A

reduced blood volume so increased conc of sodium

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9
Q

what part of the body secretes ADH?

A

Posterior pituitary

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10
Q

Give the function of ADH

A

Acts aquaporin type 2 channels on the collecting duct and DCT
causes increase in water retention

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11
Q

What does urine osmolality measure?

A

how concentrated the urine is

a higher osmolality means a higher concentration

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12
Q

How would u differentiate between CDI and NDI?

A

Water deprivation test
Give IM desmopressin after urine shown to be dilute
Desmopression acts like ADH
If urine osmolality increases, kidneys are responding and shows the cause is CRANIAL
If urine osmolality stays dilute despite desmopression - NEPHROGENIC

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13
Q

What is the treatment of cranial DI?

A

Oral desmopressin - synthetic analogue of ADH

Find cause: MRI head, test anterior pituitary (look for tumour that could affect post)

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14
Q

What is the treatment of nephrogenic DI?

A

Treat cause
Thiazide diuretics - oral bendroflumethiazide
NSAIDs - lower urine volume + plasma Na+

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15
Q

What is the emergency management of DI?

A 
Urgent plasma U&amp;E, serum + urine osmolalities
Monitor UO
IVI to keep up w UO 
Rx hypernatraemia 
IM desmopressin
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16
Q

Why is it important not to lower Na+ rapidly if there is severe hypernatraemia?

A

may cause cerebral oedema + brain injury

Endocrinology (21 decks)

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