Initial Treatment Approach for Myoclonus
The first-line treatment for positive myoclonus should be levetiracetam, sodium valproate, or clonazepam, with the specific choice determined by the neurophysiological classification of the myoclonus. 1
Immediate Diagnostic Evaluation Required Before Treatment
Before initiating therapy, you must determine whether the myoclonus is epileptic or non-epileptic, as this fundamentally changes your treatment approach:
- Obtain EEG monitoring in all patients with myoclonic jerks to detect associated epileptiform activity 2, 1
- Look specifically for: timing of onset (within 72 hours post-cardiac arrest suggests poor prognosis), distribution (focal vs. generalized), stimulus sensitivity, and whether jerks occur at rest, with posture, or during action 3
- Distinguish between simple myoclonus (FPR 5-11% for poor outcome) versus status myoclonus (continuous jerks >30 minutes, FPR 0% for poor outcome in post-anoxic settings) 2
- Consider continuous EEG if status epilepticus is suspected to monitor treatment effects 1
Treatment Algorithm Based on Neurophysiological Classification
For Cortical Myoclonus (Most Common Type)
Start with levetiracetam as first-line therapy: 1, 4, 5
- Adults: Begin 500 mg twice daily, increase by 1000 mg/day every 2 weeks to target dose of 3000 mg/day (1500 mg twice daily) 6
- Pediatric patients (≥4 years): Start 10 mg/kg twice daily, increase by 20 mg/kg/day every 2 weeks to target 60 mg/kg/day (30 mg/kg twice daily) 6
- Levetiracetam is FDA-approved for myoclonic seizures in patients ≥12 years with juvenile myoclonic epilepsy 6
Alternative first-line options if levetiracetam fails or is not tolerated:
- Sodium valproate: effective for cortical myoclonus 1, 4, 5
- Clonazepam: useful across all myoclonus types 4, 5, 3
For Cortical-Subcortical Myoclonus (Myoclonic Seizures)
Prioritize valproic acid as the mainstay of therapy for epileptic syndromes like juvenile myoclonic epilepsy, with other medications serving adjunctive roles 4, 5
For Subcortical-Nonsegmental Myoclonus
Use clonazepam as primary treatment, though numerous other agents may be needed depending on the specific etiology 4, 5
For Segmental and Peripheral Myoclonus
These are often treatment-resistant:
- Trial clonazepam first 4, 5
- Consider botulinum toxin injections for focal presentations with variable success 4, 5, 3
Special Considerations for Post-Anoxic Myoclonus (Post-Cardiac Arrest)
This context requires specific management:
- Propofol is effective for suppressing post-anoxic myoclonus and should be considered as a first-line agent for both clinical seizures and epileptiform EEG activity 7
- Sodium valproate, levetiracetam, clonazepam, benzodiazepines, and barbiturates are all treatment options 1, 7
- Do NOT use routine seizure prophylaxis in post-cardiac arrest patients due to risk of adverse effects and poor response 1, 7
- Some patients with early-onset prolonged myoclonus may evolve into Lance-Adams syndrome with good neurological recovery despite initial presentation—avoid excessively aggressive treatment in these cases 2, 1, 7
Critical Pitfalls to Avoid
- Never use myoclonus alone (without status myoclonus) to predict poor neurological outcomes due to unacceptably high false positive rates (5-11%) 2
- Phenytoin is frequently ineffective for post-anoxic myoclonus and should not be considered first-line 7
- Do not rely on motor examination findings alone (absent movements or extensor posturing) for prognostication, as they have unacceptable false positive rates of 10-15% 2
- Recognize that polytherapy with multiple drugs in large dosages is usually needed, as single agents rarely control myoclonus adequately 3, 8
- Be aware that treatment is commonly limited by side effects and variable efficacy 4, 5, 9
Renal Dosing Adjustments
For patients with impaired renal function receiving levetiracetam: