SIADH DDx

SIADH = Syndrome of inappropriate antidiuretic hormone secretion

Important cause of HYPOnatraemia

Diagnosis requires

• Presence of
  • HYPOnatraemia
  • Euvolaemia (normovolemia)
  • High urinary sodium (>20 mmol/L)
  • Urine osmolality > plasma osmolality
    • Serum osmolality <280 mmol/kg (hypotonic HYPOnatremia)
    • Urine osmolality >500mmol/kg (inappropriately concentrated)
• Absence of
  • Abnormal renal, cardiac, thyroid, adrenal hepatic function
  • Hypervolaemia (oedema)
  • NOT on a diuretic

Cause

• Malignancy
  • Small cell lung, pancreas, prostate, leukaemia, cervical
• Central Nervous System (CNS)
  • Tumour
  • Trauma (Head injury, SAH, SDH)
  • Infection (encephalitis, abscess)
  • Vascular (CVA, aneurysm, vasculitis)
  • Other (GBS, MS, DT)
• Respiratory
  • Tumour
  • Infection (aspergillosis, pneumonia, abscess)
  • COPD, CF
• Drugs
  • Opiates
  • Psychotropic (TCA, MAOI, SSRI)
  • Cytotoxic, chemotherapeutic

Correction

• Corrected with water restriction 500-1000ml/day
• Does not respond to Na replacement

References and Links

• CCC – Hypernatraemia
• CCC – Hypernatraemia Mind map (PDF)
• CCC – Hyponatraemia
• CCC – Hyponatraemia Mind map (PDF)
• CCC – Hyponatraemia Interpretation (PNG)
• CCC – SIADH – SIADH DDx
• CCC – Diabetes Insipidus Central – Diabetes Insipidus DDx
• Case – Exercise-associated Hyponatremia
• Case – Seizures, hyponatremia and ADH