SIADH

Question 1

define SIADH?

Answer 1

characterised by continued secretion of ADH, characterised by hyponatraemia secondary to the dilutional effects of excessive water retention

Question 2

what are causes of SIADH?

Answer 2

Malignancy	
•	small cell lung cancer
•	also: pancreas, prostate
Neurological
•	stroke
•	subarachnoid haemorrhage
•	subdural haemorrhage
•     meningitis/encephalitis/abscess
Infections
•	tuberculosis
•	pneumonia
Drugs	
•	sulfonylureas*
•	SSRIs, tricyclics
•	carbamazepine
•	vincristine
•	cyclophosphamide
Other causes	
•	positive end-expiratory pressure (PEEP)
•	porphyrias
•	alcohol withdrawl

Question 3

summarise the epidemiology of SIADH?

Answer 3

• Hyponatraemia is the MOST COMMON electrolyte imbalance seen in hospital

Question 4

what are the presenting symptoms of SIADH?

Answer 4

• Mild hyponatraemia may be ASYMPTOMATIC
• Headache
• Nausea/vomiting
• Muscle cramp/weakness
• Irritability
• Confusion
• Drowsiness
• Convulsions
• Coma
• Symptoms of underlying cause

Question 5

signs of SIADH on physical examination?

Answer 5

• MILD hyponatraemia - no signs
• SEVERE hyponatraemia:
o Reduced reflexes
o Extensor plantar reflexes

Question 6

what investigations should be undertaken for SIADH?

Answer 6

o Low serum sodium
o Creatinine (check renal function)
o Glucose, serum protein and lipids

Question 7

what is pseudohyponatraemia?

Answer 7

when the sodium concentration is actually normal but is erroneously reported as being low because of the presence of either hyperlipidaemia or hyperproteinaemia

Question 8

what investigation results will confirm SIADH?

Answer 8

o Low plasma osmolality
o Low serum Na+ concentration
o High urine osmolality
o High urine Na+

Question 9

management plan for SIADH?

Answer 9

• Fluid restriction
• Vasopressin receptor antagonists
• In SEVERE cases - slow IV hypertonic saline and furosemide with close monitoring

Question 10

when does central pontine myelinolysis occur ?

Answer 10

occurs with rapid correction of hyponatraemia

Question 11

what is central pontine myelinolysis characterised by?

Answer 11

• Quadriparesis
• Respiratory arrest
• Fits

Question 12

prognosis for SIADH?

Answer 12

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