Syndrome of inappropriate antidiuretic hormone (SIADH) Flashcards
What does SIADH refer to?
An increased release of antidiuretic hormone from the posterior pituitary
Increased water reabsorption from the urine that dilutes the blood leads to what?
Hyponatraemia
What are the two potential sources of too much antidiuretic hormone?
Increased secretion by the posterior pituitary
Ectopic ADH - commonly due to small cell lung cancer
How is blood diluted by excessive ADH?
Due to increased water reabsorption in the collecting ducts
What does SIADH commonly result in?
Euvolemic hyponatraemia
What happens to the urine of patients with SIADH?
Urine becomes more concentrated
Give the expected urine osmolality and urine sodium levels in patients with SIADH?
High urine osmolality
High urine sodium
What are typical clinical presentations of SIADH?
Headache
Fatigue
Muscle aches and cramps
Confusion
What can be seen in patients with severe hyponatraemia?
Seizures
Reduced consciousness
Give some causes of SIADH?
Post-operative
Lung infection
Brain pathologies
Medication - SSRIs, carbamazepine
Malignancy - small cell lung cancer
HIV
What are the clinical features of SIADH?
Euvolemia
Hyponatraemia
Low serum osmolality
High urine sodium
High urine osmolality
Why is it essential to correct sodium levels slowly?
To prevent osmotic demyelination
What non-medical approach might be able to correct hyponatraemia?
Fluid restriction
What medications can be used to manage SIADH by blocking ADH receptors?
Vasopressin receptor antagonists
