Endocrinology - SIADH Flashcards

1
Q

What does ADH do?

A

It stimulates water reabsorption from the collecting ducts in the kidney

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2
Q

What can cause SIADH?

A

This may be the result of the posterior pituitary secreting too much ADH

Or ectopic ADH secretion e.g. small cell lung cancer.

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3
Q

What occurs in SIADH?

A

Excessive ADH results in excessive water reabsorption

The water dilutes sodium causing hyponatraemia

The excessive water reabsorption is not usually significant enough to cause a fluid overload, therefore you end up with a “euvolaemic hyponatraemia”.

Urine becomes more concentrated as less water excreted by the kidneys, so:
- High urine osmolality and high urine sodium

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4
Q

Symptoms of SIADH

A

Non-specific

Headache
Fatigue
Muscle aches and cramps
Confusion
Severe hyponatraemia can cause seizures and reduced consciousness
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5
Q

Causes of SIADH

A

Post-operative from major surgery

Infection, particularly atypical pneumonia and lung abscesses

Head injury

Medications;

  • Carbamazepine
  • PPIs
  • Antipsychotics
  • SSRIs
  • Cyclophosphamide
  • NSAIDs

Malignancy, particularly small cell lung cancer
Meningitis

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6
Q

Initial diagnosis

A
  • Clinical examination will show euvolaemia
  • U&Es - hyponatraemia
  • Urine sodium and osmolality high

SIADH is a diagnosis of exclusion

Other causes of hyponatraemia need to be excluded:

  • Negative short synacthen test to exclude adrenal insufficiency
  • No history of diuretic use
  • No diarrhoea, vomiting, burns, fistula or excessive sweating
  • No excessive water intake
  • No chronic kidney disease or acute kidney injury
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7
Q

Hyponatraemia and history of smoking/weight loss think…

A

Small cell lung cancer secreting ADH (causing SIADH)

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8
Q

Management of SIADH

A

Investigate for and treat the underlying cause

Stop causative medications

Correct sodium slowly

Fluid restriction for SIADH (500ml-1L fluid intake)

Tolvaptan can be used in refractory cases under guidance from specialist (vaptans are ADH receptor blockers)

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9
Q

First step in assessing hyponatraemia

A

Assess the fluid status

Hypovolaemic - e.g. diuretics, poor fluid intake, increased loss

Euvolaemic - SIADH

Hypervolaemic - e.g. heart, liver and renal failure

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10
Q

Management of symptomatic hyponatraemia

A

Correct with 3% hypertonic saline under senior guidance

Do not correct sodium too quickly (not more that 10mmol per 24h)

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11
Q

What is the risk of correcting sodium too quickly?

A

Osmotic demyelination syndrome

Due to shifts in the osmolality in the neurone, the neurone undergoes demyelination

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12
Q

How does osmotic demyelination syndrome present? What is the treatment?

A

This may present as spastic quadriparesis, pseudobulbar palsy and cognitive and behavioural changes.

There is a significant risk of death.

Treatment is only supportive if this occurs and most are left with some neurological deficit so prevention is key.

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