SIADH Flashcards

1
Q

What is SIADH?

A

Continued secretion of ADH, despite the absence of normal stimuli for secretion (i.e. increased serum osmolality or decreased blood volume)

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2
Q

List broad areas that when effected can lead to SIADH

A
Brain
Lungs
Drugs
Tumours
Metabolic state
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3
Q

List 6 “brain” related causes of SIADH

A
Haemorrhage/thrombosis  
Meningitis 
Abscess 
Trauma  
Tumour  
Guillain-Barre syndrome
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4
Q

What 4 pulmonary pathologies can lead to SIADH?

A

Pneumonia
TB
Abscess
Aspergillosis

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5
Q

What cancerous pathologies can lead to SIADH?

A
Small cell lung caner  
Breast cancer 
Lymphoma  
Leukaemia  
Pancreatic cancer 
Prostate cancer 
Mesothelioma 
Sarcoma 
Thymoma
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6
Q

List 4 drugs that may lead to SIADH

A

Vincristine
Opiates
Carbamazepine
Chlorpropamide

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7
Q

What metabolic states may lead to SIADH?

A

Porphyria

Alcohol withdrawal

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8
Q

Describe the epidemiology of SIADH

A

Hyponatraemia is the MOST COMMON electrolyte imbalance seen in hospital
< 50% of severe hyponatraemia is caused by SIADH

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9
Q

List 9 symptoms of SIADH

A
Headache  
N+V 
Muscle cramp/ weakness 
Irritability  
Confusion  
Drowsiness  
Convulsions  
Coma  
Symptoms of underlying cause
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10
Q

List signs of severe hyponatraemia

A

Reduced reflexes
Extensor plantar reflexes
Signs of underlying cause

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11
Q

What is the hyponatraemia caused by in SIADH?

A

Dilution from excessive water reabsorption + not due to a decrease in total body Na+

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12
Q

Why does SIADH cause a euvolaemic hyponatraemia?

A

Hypervolaemia causes heart distention, so BNP + ANP are secreted which cause salt+ water extcretion

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13
Q

What investigations are performed in suspected SIADH?

A

Serum sodium
Serum osmolarity
Serum urea
Urine osmolarity
Creatinine (check renal function)
Glucose, serum protein + lipids: to exclude pseudohyponatraemia
Free T4 + TSH: hypothyroidism can cause hyponatraemia
Short synACTHen test: adrenal insufficiency can cause hyponatraemia

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14
Q

What is Pseudohyponatraemia?

A

When Na+ concentration is actually normal but is erroneously reported as being low because of the presence of either hyperlipidaemia or hyperproteinaemia

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15
Q

Describe the results necessary for diagnosis of SIADH

A
Low plasma osmolality  
Low serum Na+ conc.
High urine osmolality 
High urine Na+  
\+ Absence of hypovolaemia, oedema, renal failure, adrenal insufficiency + hypothyroidism
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16
Q

List 3 investigations that may be used to identify the cause of SIADH

A

CXR
CT
MRI

17
Q

Describe the management of SIADH

A

1st line: Treat underlying cause
1st line: Fluid restriction to 1L per day
2nd line: Vasopressin receptor antagonists (e.g. tolvaptan)
3rd line: NaCl + furosemide
4th line: demeclocycline

18
Q

List 4 complications of SIADH

A

Convulsions
Coma
Death
Central pontine myelinolysis

19
Q

What is the prognosis of SIADH?

A

Depends on the CAUSE
Na+ < 110 mmol/L is associated with a HIGH MORBIDITY + MORTALITY
50% mortality with central pontine myelinolysis

20
Q

What is Central pontine myelinolysis? What is it caused by? What is it characterised by?

A
Demylination of pons
Occurs with rapid correction of hyponatraemia  
Quadriparesis  
Respiratory arrest  
Fits
21
Q

Describe the treatment of SIADH in severe/ acute cases

A

Slow IV hypertonic saline + furosemide with close monitoring