Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)

• Impaired water excretion caused by the inability to suppress the secretion of antidiuretic hormone
• Hyponatremia
• Hypo-osmolality
• Urine osmolality > 100 mosmol/kg
• Urine Na+ > 40 meq/L
• Serum K+ normal
• Serum Uric acid low

Causes

• CNS disorder - stroke, hemorrhage, infection, trauma, psychosis
• Ecoptic production - small cell lung carcinoma
• Medications - chlorpropamide, carbamazepine/oxcarbazepine, cyclophosphamide, SSRI, etc
• Iatrogenic - vasopressin, dDAVP, oxytocin
• Infections - PNA, HIV

Treatment

• Treat underlying disease
• Raise Na+ levels (generally < 9 meq/L per 24 hours)
• Fluid restriction (<800 mL / day)
• Hypertonic saline (SAH, neurologic symptoms - caution for osmotic demyelination)
• Oral salt tablets
• Loop diuretic (i.e. furosemide) to increase water excretion
• Vasopressin receptor antagonists