How to manage myoclonus after subarachnoid (spinal) block?

Management of Myoclonus After Subarachnoid Block

For myoclonus following subarachnoid (spinal) block, first-line treatment should include benzodiazepines such as clonazepam, followed by antiepileptic medications like levetiracetam or sodium valproate if benzodiazepines are ineffective. 1, 2

Clinical Assessment and Immediate Management

• Assess severity and pattern:

  • Determine if myoclonus is focal, multifocal, or generalized
  • Evaluate if movements are continuous (status myoclonus) or intermittent
  • Monitor for respiratory compromise or desaturation

• Initial interventions:

  1. Benzodiazepines: Start with IV clonazepam (first-line for subcortical/brainstem myoclonus) 1, 2
  2. Respiratory support: Provide supplemental oxygen and monitor oxygen saturation closely
  3. Hemodynamic monitoring: Check vital signs frequently, especially if sedatives are administered

Pharmacological Management Algorithm

1. First-line therapy:

   • Clonazepam: 0.5-2 mg IV initially, may repeat as needed 2
   • If ineffective after 10-15 minutes, proceed to second-line therapy

2. Second-line therapy:

   • Levetiracetam: 500-1000 mg IV (effective for post-anoxic myoclonus) 1, 2
   • Sodium valproate: 20-40 mg/kg IV loading dose (avoid in women of childbearing age) 2

3. For refractory cases:

   • Propofol: Consider for severe, persistent myoclonus requiring immediate suppression 1, 2
   • General anesthesia with neuromuscular blockade may be necessary in extreme cases 3, 4

Diagnostic Evaluation

• EEG monitoring: Consider intermittent or continuous EEG to determine if myoclonus has epileptiform correlates 1, 2

• Laboratory tests: Check electrolytes, glucose, calcium, and magnesium levels to rule out metabolic causes 3, 4

• Neuroimaging: Consider brain and spinal MRI if myoclonus persists beyond 24 hours to rule out structural lesions 2

Special Considerations

• Medication-induced myoclonus: Intrathecal bupivacaine has been reported as a potential cause of spinal myoclonus 3, 4

• Opioid-induced myoclonus: If intrathecal opioids were used, they may contribute to myoclonus development 5, 6

  • Consider opioid rotation or dose reduction if this is suspected

• Duration of treatment: Myoclonus following subarachnoid block may resolve spontaneously within 24-48 hours, but some cases may require prolonged treatment 3, 4

Monitoring and Follow-up

• Continuous monitoring: For the first 24 hours, especially if status myoclonus is present 1

• Prolonged observation: Necessary after treatment of seizures, especially in patients with status myoclonicus 2

• Reassessment: Evaluate response to therapy every 2-4 hours and adjust treatment accordingly

Cautions and Pitfalls

• Avoid phenytoin and carbamazepine: These can paradoxically worsen cortical myoclonus 2

• Respiratory depression: Monitor closely when using multiple sedative medications

• Distinguish from seizures: Myoclonus may be mistaken for seizure activity; EEG can help differentiate 1, 2

• Rule out Lance-Adams syndrome: If myoclonus persists after recovery from anesthesia, consider this diagnosis, which requires long-term management 2

Myoclonus after subarachnoid block is rare but can be distressing for both patient and provider. Prompt recognition and appropriate treatment are essential to prevent complications and ensure patient comfort.