Hyponatremia

Epidemiology

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Etiology

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Pathophysiology

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Clinical features

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Diagnostics

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Treatment

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Complications

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Osmotic demyelination syndrome (ODS)

• Definition: damage to the myelin sheath of the white matter in the CNS caused by a sudden rise in serum osmolality
• This osmotic gradient pulls water out of brain cells, leading to cell shrinkage, apoptosis, and stripping of myelin sheaths (demyelination), particularly of oligodendrocytes.
• The pons is uniquely susceptible due to its compact structure of gray and white matter, leading to the classic presentation of Central Pontine Myelinolysis (CPM).
• Causes
  • Iatrogenic: rapid correction of chronic hyponatremia
    • High-risk factors for ODS: alcohol use disorder (Malnutrition & Low Solute Intake), malnutrition, liver disease, hypokalemia, initial sodium concentration ≤ 105 mEq/L
  • Rapid changes in other osmotically active solutes (e.g., glucose)
• Clinical features
  • Biphasic course: Initial improvement from hyponatremia correction, followed by neurologic deterioration 2-6 days later.
  • Classic Pontine Sx: Spastic quadriplegia, pseudobulbar palsy (dysarthria, dysphagia), and potentially “locked-in” syndrome.
• Diagnostics
  • MRI brain: T2-hyperintense (bright) signal in the central pons.
    • Rapid Na+ Correction → Oligodendrocyte Death → Demyelination → Tissue Breakdown → Edema (↑ Free Water) → ↑ T2 Signal → Hyperintensity (Brightness) on MRI