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Snapshot
  • SCLCA 48-year-old female presents to the emergency room with mental status changes. Laboratory analysis of the patient's serum shows: Na+ 122 mEq/L, K+ 3.9 mEq/L, HCO3- 24 mEq/L, BUN 21 mg/dL, Creatinine 0.9 mg/dL, Ca2+ 8.5 mg/dL, Glucose 105 mg/dL. Urinalysis shows: Osmolality 334 mOsm/kg, Na+ 45 mEq/L, Glucose 0 mg/dL. Sputum cytology is shown.
Introduction
  • SIADH is a syndrome characterized by an
    • increased ADH production
    • an increased sensitivity to ADH
  • Pathogenesis
    • causes
      • paraneoplastic syndromes
        • small cell carcinoma of the lung  
          • cancer cells produce ADH ectopically
      • CNS disturbances
        • infection, stoke, tumor, trauma, hydrocephalus
      • may also be cause by drugs
        • NSAIDS, antidepressants, chemotherapy, clofibrate, narcotics, carbamazepine
Presentation
  • Symptoms
    • mental status changes 
      • caused by cerebral edema
Evaluation
  • Labs 
    • hyponatremia
      • secondary to dilutional effects of increase water resorption
      • ADH increases aquaporin insertion in the collecting duct of the renal tubule
    • urine osmolality > 100 mOsm/kg
      • urine is always concentrated despite decreasing serum osmolarity
    • serum osmolality < 275 mOsm/kg
    • random urine sodium > 40 mEq/L
Treatment
  • Moderat symptoms - Lifestyle
    • fluid restriction (not salt restriction)
  • Moderate - severe symptoms - Pharmacologic
    • demeclocycline
      • induces ADH insensitivity
        • specifically works at the vasopression type-2 receptor (V2R) 
      • can be used in patients with small cell carcinoma
      • not routinely used
    • conivaptan, tolvaptan
      • ADH antagonist
    • consider hypertonic saline (use cautiously)
    • normal saline + diuretic (furosemide)
Complications
  • Central pontine myelinolysis (CPM)
    • result of too rapid correction of hyponatremia
 

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