Endocrine - SIADH Flashcards

1
Q

What is Syndrome of inappropriate antidiuretic hormone?

A

Increased ADH from posterior pituitary

Increased water reabsorption from urine, diluting the blood causing hyponatraemia

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2
Q

What are the potential sources of excess ADH?

A
  • Increased secretion by posterior pituitary
  • Ectopic ADH via small cell lung
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3
Q

Outline SIADH pathophysiology

A

Excessive ADH causes increased water reabsorption in collecting ducts, diluting blood

This causes dilutional hyponatraemia

Extra water is not enough to cause fluid overload

SIADH results in euvolaemic hyponatraemia

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4
Q

Why do patients with SIADH have high urine osmolality and high urine sodium?

A

Urine becomes more concentrated as kidneys excrete less water

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5
Q

How do patients with SIADH present?

A

Symptoms relate to hyponatraemia
- Headache
- Fatigue
- Muscle aches and cramps
- Confusion

Severe hyponatraemia
- Seizures
- Reduced consciousness

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6
Q

What are the causes of SIADH?

A

SIADH

Small cell lung cancer
Infection- pneumonia and lung abscesses
After surgery (post-op)
Drugs (SSRIs+ carbamazepine)
HIV

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7
Q

How do you diagnose SIADH?

A

Euvolaemia
Hyponatraemia
Low serum osmolality
High urine sodium
High urine osmolality

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8
Q

What causes of hyponatraemia must be excluded?

A

Adrenal insufficiency
No diuretic use
No CKD
No HF
No liver disease
No excessive water intake

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9
Q

What is primary polydipsia?

A

Excessive water consumption with no underlying cause

Dilutes blood and urine

Euvolaemic hyponatraemia

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10
Q

What imaging is used for SIADH?

A

CXR- for infection and lung cancer

CTtap
MRI head
Both to find the malignancy

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11
Q

How is SIADH managed?

A

Treat underlying cause
Fluid restriction
Vasopressin receptor antagonists (tolvaptan)- causes rapid sodium rise

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12
Q

Why do you correct sodium slowly in SIADH?

A

Osmotic Demyelination Syndrome

AKA

Central pontine myelinolysis

Complication of long-term severe hyponatraemia

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13
Q

What is osmotic demyelination syndrome?

A

As blood sodium drops water moves across the BBB

As the brain has a high concentration of solutes this causes the brain to swell with fluid

Brain adapts by reducing solutes to balance water across the BBB

So if hyponatraemia has been present and severe for a long time, brain cells with have low osmolality

First phase
Rapid rise causes sudden shift of water

Patient presents as encephalopathic and confused

Vomiting, headaches and seizures

Second phase
Demyelination of neurones in the pons

Occurs a few days after rapid correction of sodium

  • Spastic quadriparesis
  • Pseudobulbar palsy
  • Cognitive and behavioural changes
  • Significant risk of death

Prevent as treatment is only supportive
Most patients will have neurological deficit after

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