Diabetes Insipidus Flashcards

1
Q

What is diabetes insipidus?

A

Diabetes insipidus is a rare condition causing polyuria and polydipsia. Diabetes insipidus is not related to diabetes but share common signs and symptoms.

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2
Q

Describe the two types of DI?

A

Cranial: Impaired ability to secrete enough AVP
Nephrogenic: Normal AVP production, but nephrons cant respond to it

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3
Q

Describe the primary and acquired aetiology of central DI

A

Primary causes include genetic, e.g. DIDMOAD syndrome), or developmental syndromes (septo-opticdysplasia).
The acquired causes include tumours (germ cell tumours), trauma, inflammatory, vascular (aneurysm)

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4
Q

Describe the primary and acquired causes
of nephrogenic
central DI

A

The primary causes are typically genetic, e.g. X-linked recessive V2-R
The acquired causes include CKD, metabolic cause (hypercalcaemia, hypokalaemia), drug induced, osmotic diuresis, systemic disorder (amyloidosis)

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5
Q

What is the first step to diagnosing DI?

A

The first is to establish the presence of polydopsia and poluria using a 24hr urine collection. Patient testing positives will show >40mL/Kg per 24hr in adults, and >100mL/Kg per 24h in infants

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6
Q

What blood and urine tests will help diagnose DI?

A

They will be used to rule out more common causes of polydipsia and polyuria, using serum calcium, plasma glucose, serum potassium. Best test is to perform a random paired serum and urine osmolality test

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7
Q

What paired serum and urine osmolality test results indicate DI?

A

A patient presenting with a urine osmolality of >750mOsm/kg is unlikely to have DI, as the patient can appropriately concentrate their urine. Whereas a raised serum osmolality accompanied with a low urine osmolality indicate strong clinical suspicion for DI.

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8
Q

Diagnosis of DI using water deprivation test

A

If urine osmolality is still <750mosm/kg after 8h fluid restriction a desmopressin test (artificial AVP) will be carried out. Nephrogenic DI will show no response whilst cranial achieves normal concentration of urine

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9
Q

What direct testing for DI is available?

A

This can be done using AVP/copeptin measurements. Hypertonic saline infusion given till serum sodium reaches 150mmol/L. Serum plasma samples taken for AVP/copeptin measurement under osmotic stimulus. Central DI patients will present a sub-normal (flat response) AVP/copeptin response to osmotic stimulus. Nephrogenic DI will present a high basal AVP/copeptin or exaggerated response

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10
Q

Why is copeptin a good measure for diagnosing DI?

A

It is derived from the pre-pro-hormone of AVP. Thus AVP and copeptin are produced equimolarly. It is an easier measure than AVP and has a quicker turnaround

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11
Q

How can DI be differentiated?

A

Using copeptin. Copeptin of <5pmol/L is likely to be CDI. Whereas copeptin of >5pmol/L shows CDI to be unlikely. Copeptin usually markedly elevated in NDI as the AVP is still secreted, but due to nephron resistance can’t act on it.

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12
Q

Treatment of DI

A

Central DI is treated using hormone replacement, such as ddAVP in tablets or as a nasal spray. Whereas nephrogenic DI is more complicated and is dependent on the underlying cause but can be treated by withdrawing medication if medication is related, thiazide diuretics/NSAIDs, ensure adequate hydration

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