How do you differentiate and treat seizures versus myoclonus?

Differentiating and Treating Seizures versus Myoclonus

Myoclonus in syncope is asynchronous, asymmetrical, begins after loss of consciousness (typically 20 seconds later), and involves few movements (~10), whereas epileptic seizures feature synchronous movements beginning at onset of unconsciousness, last longer (mean 74-90 seconds), and involve many movements that cannot be counted. 1

Clinical Differentiation

Timing and Movement Characteristics

• Onset relative to loss of consciousness: Epileptic myoclonus begins at the onset of unconsciousness, while syncope-related myoclonus typically begins approximately 20 seconds after onset of loss of consciousness 1

• Movement pattern: Symmetrical and synchronous movements indicate epilepsy, whereas asymmetrical and asynchronous movements suggest syncope (though may rarely be epilepsy) 1

• Number of movements: Few movements (approximately 10 or so) make syncope far more likely than epilepsy, while many movements ("100", "cannot count") indicate epilepsy 1

• Duration of unconsciousness: If measured, loss of consciousness <30 seconds makes syncope far more likely, while duration >1 minute suggests epileptic seizure (mean 74-90 seconds for seizures versus mean 20 seconds for syncope) 1

Additional Distinguishing Features

• Movement distribution: Movements restricted to one limb or one side indicate epilepsy rather than syncope 1

• Stertorous (snoring) breathing: Epileptic seizures are more likely than psychogenic non-epileptic seizures to have this feature; syncope only shows this briefly (10 seconds) in deep hypoperfusion 1

• Head turning: Prolonged head turning suggests epileptic seizures, while syncope with deep hypoperfusion shows head turning lasting <30 seconds 1

• Eye position: Eyes open during unconsciousness suggests epilepsy or syncope (only closed in shallow and short-lasting syncope), while eyes closed during unconsciousness suggests psychogenic pseudosyncope 1

Terminology Clarification

• The term "clonic" is restricted to epilepsy in everyday use, while "myoclonus" describes movements in both syncope and certain epilepsy types, as well as postanoxic movements 1

• "Convulsions" should be reserved for epilepsy, while "myoclonic jerks" has little connotation with a specific cause and should be used cautiously to avoid unwarranted conclusions 1

Types of Epileptic Myoclonus

• Cortical epileptic myoclonus represents a fragment of partial or symptomatic generalized epilepsy 2

• Thalamo-cortical epileptic myoclonus is a fragment of idiopathic generalized epilepsy 2

• Reflex reticular myoclonus represents fragments of hypersynchronous epileptic activity of neurons in the brainstem reticular formation 2

• Myoclonus is commonly associated with reflex seizures in idiopathic generalized epilepsies, most frequently triggered by visual stimuli including flashing lights or patterns, but also by movement, speech, reading, calculations, and praxis 3

Post-Cardiac Arrest Context

• Myoclonus occurs in 18-25% of post-cardiac arrest patients who remain comatose, making it the most common seizure type in this population 1

• Clinical myoclonus may or may not be of epileptic origin, and other motor manifestations could be mistaken for seizures 1

• Post-anoxic status epilepticus was detected in 23-31% of comatose cardiac arrest patients using continuous EEG monitoring with inclusive EEG criteria 1

• EEG is essential to distinguish epileptic from non-epileptic myoclonus in post-cardiac arrest patients, as the majority of myoclonus types are non-epileptic 1

• Myoclonus occurring with continuous cortical background activity on EEG (subcortical myoclonus) may not warrant aggressive antiseizure treatment if not interfering with mechanical ventilation 1

Diagnostic Approach

EEG Monitoring

• Use intermittent EEG to detect epileptic activity in patients with clinical seizure manifestations 1

• Consider continuous EEG to monitor patients with diagnosed status epilepticus and treatment effects 1

• Continuous EEG increases sensitivity to detect epileptiform activity including seizures and status epilepticus after cardiac arrest compared with brief intermittent recordings, due to the episodic and unpredictable nature of these patterns 1

• Focal seizures show ictal discharges originating from one hemisphere on EEG 4

Tilt-Table Testing

• Tilt-table testing is reasonable to distinguish convulsive syncope from epilepsy when detailed history cannot clearly determine whether convulsive movements were secondary to syncope 1

• Approximately 50% of patients with either questionable or drug-refractory epilepsy have positive tilt-table tests suggestive of vasovagal etiology 1

• Prolonged convulsions and marked postictal confusion are uncommon in syncope with convulsive movements, though fatigue is frequent after reflex syncope and may be confused with a postictal state 1

Treatment Approach

Treating Epileptic Seizures and Myoclonus

• Treat clinical seizures including myoclonus with sodium valproate, levetiracetam, phenytoin, benzodiazepines, propofol, or a barbiturate to prevent potential exacerbation of brain injury 1

• Myoclonus can be particularly difficult to treat; phenytoin is often ineffective 1

• Propofol is effective to suppress post-anoxic myoclonus 1

• Clonazepam, sodium valproate, and levetiracetam are antimyoclonic drugs that may be effective in post-anoxic myoclonus 1

• After the first seizure event, start maintenance therapy once potential precipitating causes (intracranial hemorrhage, electrolyte imbalance) are excluded 1

Levetiracetam Dosing

• For myoclonic seizures in patients ≥12 years with juvenile myoclonic epilepsy: Initiate at 1000 mg/day (500 mg BID), increase by 1000 mg/day every 2 weeks to recommended dose of 3000 mg/day 5

• For partial onset seizures in adults: Initiate at 1000 mg/day (500 mg BID), with additional increments of 1000 mg/day every 2 weeks to maximum 3000 mg/day 5

• Levetiracetam is effective as adjunctive therapy for myoclonic seizures, with 60.4% responder rate (≥50% reduction) versus 23.7% for placebo 5

Drugs to Avoid

• Avoid phenytoin, carbamazepine, oxcarbazepine, lamotrigine, vigabatrin, tiagabine, gabapentin, and pregabalin as these are known to aggravate myoclonus or myoclonic seizures 6

Emergency Treatment

• Emergency treatment of motor status consists of intravenous administration of benzodiazepines, valproate, or levetiracetam 6

Prophylaxis Considerations

• Routine seizure prophylaxis in post-cardiac arrest patients is not recommended due to risk of adverse effects and poor response to antiepileptic agents among patients with clinical and electrographic seizures 1

• Whether systematic detection and treatment of electrographic epileptic activity improves patient outcome is not known 1

Prognostic Implications

• Myoclonus and electrographic seizure activity, including status epilepticus, are related to poor prognosis, but individual patients may survive with good outcome 1

• Cardiac arrest survivors who have continuous cortical background activity and those who develop epileptiform abnormalities >24 hours after ROSC are more likely to recover 1

• Prolonged observation may be necessary after treatment of seizures 1