Syndrome of Inappropriate Antidiuretic Hormone

(SIADH)

• accounts for 14-40% of cases of hyponatraemia

Diagnosis

• true extracellular fluid hypo-osmolality
• urinary osmolality inappropriately high
• clincally euvolaemic
• high urinary sodium excretion
• thyroid and adrenal dysfunction ruled out

Aetiology

• Small cell carcinoma of bronchus
• Central nervous system tumours
• Drug induced SIADH
  • e.g. selective serotonin re-uptake inhibitors (SSRIs)

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