Syndrome of inappropriate antidiuretic hormone

Syndrome of inappropriate antidiuretic hormone (SIADH) is defined as euvolaemic, hypotonic hyponatraemia secondary to impaired free water excretion, usually from excessive arginine vasopressin (AVP) release.

Severe neurological symptoms, such as altered mental status, seizure, and coma, may result from SIADH and these are always treated with hypertonic saline, with close monitoring to avoid overcorrection of serum sodium.

Central pontine myelinolysis (osmotic demyelination syndrome) may occur with rapid correction of serum sodium in excess of 12 mmol/L/day (12 mEq/L/day).

Vasopressin receptor antagonists (also known as vaptans) are a class of medicines that compete with the antidiuretic hormone AVP for binding at the vasopressin receptor, permitting free water excretion.

The syndrome of inappropriate antidiuretic hormone (SIADH) is characterised by hypotonic hyponatraemia, concentrated urine, and a euvolaemic state. The impairment of free water excretion is caused by increased arginine vasopressin (antidiuretic hormone or AVP) release. Pseudohyponatraemia due to hyperglycaemia, hyperlipidaemia, or hyperproteinaemia should be ruled out first. Renal failure, adrenal insufficiency, and appropriate release of AVP secondary to extracellular volume depletion (hypovolaemia, due to gastrointestinal or renal loss) or intravascular volume depletion (hypervolaemia due to congestive heart failure, cirrhosis of the liver, or nephrotic syndrome) must be ruled out in order to diagnose SIADH.