Syndrome of inappropriate antidiuretic hormone secretion

Background

  • Abbreviation: SIADH
  • Inappropriate or continued action of ADH despite normal/increased plasma volume→ impaired water excretion→ hyponatremia and hypo-osmolality

Clinical Features

  • See hyponatremia
  • Symptoms of neoplasm, particularly lung neoplasm

Differential Diagnosis (Causes)

Evaluation

Essential Criteria[1]

  • Effective serum osmolality <275 mOsm/kg
  • Urine specific gravity > 1.015
  • Urine osmolality >100 mOsm/kg at some level of decreased effective osmolality
  • Clinical euvolemia
  • Urine sodium concentration >30 mmol/l with normal dietary salt and water intake
  • Absence of adrenal, thyroid, pituitary or renal insufficiency
  • No recent use of diuretic agents

Supplemental criteria

  • Serum uric acid <0.24 mmol/l (<4mg/dl)
  • Serum urea <3.6 mmol/l (<21.6mg/dl)
  • Failure to correct hyponatremia after 0.9% saline infusion
  • Fractional sodium excretion >0.5%
  • Fractional urea excretion >55%
  • Fractional uric acid excretion >12%
  • Correction of hyponatremia through fluid restriction

Management[2]

  • See hyponatremia
  • Fluid restriction
  • Oral salt tablets (NaCl) for mild-moderate hyponatremia
  • 100 cc bolus of 3% NaCl for severe symptoms, repeat if neurologic symptoms persist or worsen
    • Ideally given through central line
  • DO NOT give normal saline 0.9%
    • In SIADH, sodium handling is intact and renal system will excrete Na
    • Water handling out of balance from excessive ADH
    • All sodium will be excreted, urine osmolality will remain high
    • Half of the bolus of normal saline will be retained, worsening hyponatremia
  • See osmotic demyelination syndrome for excessively rapid overcorrection

Disposition

References

  1. ↑ Schwartz WB, Bennett W, Curelop S, Bartter FC. A syndrome of renal sodium loss and hyponatremia probably resulting from inappropriate secretion of antidiuretic hormone. American Journal of Medicine 1957 23 529–542
  2. ↑ Verbalis JG et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013 Oct;126(10 Suppl 1):S1-42.
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