Post-hypoxic myoclonus

Background

• Myoclonus (irregular muscle contractions) after hypoxic brain injury due to cardiac arrest
• Acute: onset within 48h of injury
  • Post-hypoxic myoclonic status: acute myoclonus lasting >30min
    • Difficult to control, associated with poor prognosis
    • Occurs in 30-40% of comatose cardiac arrest survivors
• Chronic: onset days-weeks after cardiac arrest in patients who regained consciousness (AKA Lance-Adams syndrome)

Clinical Features

• Acute:
  • Recent (within 48h) hypoxic brain injury with neuronal necrosis
  • Abrupt onset of irregular muscle contractions, focal or generalized
• Post-hypoxic status myoclonus
  • Onset usually within 12-24h of injury
  • Generalized, multifocal clonus
• Chronic
  • Onset days-weeks after arrest
  • Awareness preserved
  • Typically intention myoclonus

Differential Diagnosis

• Seizure

Evaluation

• EEG (r/o seizure)
• Evaluate for alternative etiologies

Management

• Acute/status
  • Difficult and of limited utility
  • Consider benzodiazepines, propofol, phenytoin, valproate
  • Address goals of care given sign of poor prognosis
• Chronic/lance-adams syndrome
  • Valproate, clonazepam, and/or levetiracetam may help control myoclonus

See Also

• Hypoxemia

References

• LITFL: https://litfl.com/post-hypoxic-myoclonus/