What is the management for myoclonic jerks (clonic jerks) post cardiac arrest?

Management of Myoclonic Jerks Post-Cardiac Arrest

Propofol is the most effective first-line agent for suppressing post-anoxic myoclonus, followed by clonazepam, sodium valproate, or levetiracetam as antimyoclonic alternatives, while phenytoin should be avoided as it is often ineffective. 1, 2, 3

Initial Diagnostic Approach

Obtain EEG to distinguish epileptic from non-epileptic myoclonus, as the majority of post-anoxic myoclonus is non-epileptic and this distinction fundamentally changes both treatment approach and prognosis. 1, 3

• Use intermittent EEG to detect epileptic activity in patients with clinical myoclonic manifestations 1
• Consider continuous EEG monitoring if status epilepticus is diagnosed or to assess treatment effects, particularly in sedated patients where clinical manifestations may be masked 1
• Myoclonus occurs in 18-25% of patients who remain comatose after return of spontaneous circulation (ROSC) 1, 2

Pharmacological Treatment Algorithm

First-Line Agent

Propofol is the preferred agent for acute suppression of post-anoxic myoclonus, with proven efficacy in multiple guidelines. 1, 2, 3

• Propofol effectively suppresses both clinical myoclonus and epileptiform EEG activity 2
• Standard dosing: 2 mg/kg bolus followed by 3-7 mg/kg/hour infusion 4
• Requires mechanical ventilation and continuous monitoring 4

Alternative Antimyoclonic Agents

When propofol is contraindicated or as maintenance therapy, use:

• Sodium valproate: 20-30 mg/kg IV over 5-20 minutes, with 88% efficacy and minimal hypotension risk (0% vs 12% with phenytoin) 1, 2, 4
• Levetiracetam: 30 mg/kg IV over 5 minutes, with 68-73% efficacy and particularly effective for myoclonic seizures 1, 2, 4
• Clonazepam: Effective benzodiazepine option for myoclonus control 1, 2, 3

Agents to Avoid

Phenytoin is often ineffective for post-anoxic myoclonus and should not be used as a first-line agent. 1, 2

Critical Distinction: Lance-Adams Syndrome

Be vigilant for Lance-Adams syndrome, characterized by generalized myoclonus with epileptiform discharges that paradoxically indicates potential for good neurological recovery. 2, 4

• Lance-Adams presents with action myoclonus, cerebellar ataxia, and preserved intellect 2, 5
• This syndrome is compatible with good prognosis and should not be treated overly aggressively 2, 4
• Levetiracetam has demonstrated particular efficacy in Lance-Adams syndrome 6, 7
• Accurate distinction from myoclonic status epilepticus is vital as they have vastly different prognoses 5

Treatment Initiation and Monitoring

Start maintenance therapy only after excluding precipitating causes such as intracranial hemorrhage or electrolyte imbalances. 1

• Prolonged observation may be necessary after initiating seizure treatment 1
• Continuous EEG monitoring helps assess treatment efficacy, especially when sedation masks clinical signs 1, 3
• Titrate medications based on reduction in frequency and severity of myoclonic jerks 3

Prognostic Considerations

Status myoclonus within 72 hours after ROSC predicts poor neurological outcome with 99.8-100% specificity, but individual patients can survive with good outcomes. 1, 2, 3

• Myoclonus within 96 hours predicts poor outcome with 77.8-100% specificity but only 18.2-44.4% sensitivity 1
• Young age, presence of illicit substances, and primary respiratory causes of arrest may contribute to better outcomes despite severe initial presentation 8
• Use myoclonus as part of a multimodal prognostication approach, never in isolation 1

Common Pitfalls to Avoid

Do not use prophylactic anticonvulsants after cardiac arrest, as routine seizure prophylaxis is not recommended due to risk of adverse effects and poor response rates. 1

• Avoid confusing non-epileptic motor manifestations with true seizures—always confirm with EEG 1, 3
• Do not allow sedation and high-dose anticonvulsants to confound neurological examination and lead to overly pessimistic prognosis 2
• Prolong observation when residual sedation or paralysis may interfere with clinical assessment 1
• Recognize that neuromuscular blockers will mask myoclonus entirely and prevent accurate assessment 1, 4