What is the management and treatment approach for a patient suspected of having non-convulsive seizures?

Management and Treatment of Non-Convulsive Seizures

For patients suspected of having non-convulsive seizures, promptly perform EEG within 24 hours and treat identified seizures with standard antiseizure medications (levetiracetam, valproate, or phenytoin/fosphenytoin), as treatment of nonconvulsive seizures is reasonable and may prevent secondary brain injury. 1

Immediate Diagnostic Approach

EEG Acquisition and Timing

• Order EEG immediately for any patient who does not follow commands after a seizure or has unexplained altered mental status, as this is a Class 1 recommendation with the highest level of evidence 1
• Perform EEG within 24 hours of presentation, as early EEG (within 16 hours) detects epileptiform discharges in 52.1% of cases versus only 20.2% after 16 hours 2
• Expect an average response time of approximately 3 hours from EEG request to preliminary reading, so order early 1, 3
• Use continuous EEG monitoring rather than brief 20-30 minute recordings when feasible, as routine EEG misses approximately 50% of nonconvulsive seizures compared to prolonged monitoring 2, 4

Patient Populations Requiring Urgent EEG

• Post-cardiac arrest patients who remain comatose after return of spontaneous circulation 1
• Patients with persistent altered consciousness 60 minutes after apparent seizure termination 2, 3
• Comatose ICU patients with unexplained impairment of mental status 1, 2
• Any patient with altered mental status and history of seizures, witnessed seizure activity, or abnormal eye movements 5, 6

EEG Interpretation Framework

Diagnostic Criteria for Nonconvulsive Seizures

Use American Clinical Neurophysiology Society criteria to classify findings 1:

Electrographic Seizure:

• Epileptiform discharges averaging >2.5 Hz for ≥10 seconds, OR
• Any pattern with definite evolution (≥2 sequential changes in frequency, morphology, or location) lasting ≥10 seconds 1

Electrographic Status Epilepticus:

• Any pattern qualifying as electrographic seizure for ≥10 continuous minutes, OR
• Total duration ≥20% of any 60-minute monitoring period 1

Ictal-Interictal Continuum (possible status epilepticus):

• Periodic discharges or spike/sharp-wave patterns averaging >1.0 and ≤2.5 Hz over 10 seconds, OR
• Patterns averaging ≥0.5 Hz and ≤1.0 Hz with additional features (superimposed fast activity, rhythmic activity, or sharp waves) 1

Monitoring Duration

• Continue EEG for at least 24 hours if the patient does not return to baseline neurologic function 1
• Approximately 25% of patients have ongoing electrical seizures despite cessation of visible convulsive activity 7, 3
• In post-cardiac arrest patients, 10-35% who do not follow commands have seizures detectable only by EEG 1

Treatment Algorithm

First-Line Treatment for Identified Nonconvulsive Seizures

Treat nonconvulsive seizures detected by EEG with standard antiseizure medications (Class 2a recommendation) 1:

Preferred Initial Agents (choose one based on clinical context):

1. Levetiracetam 8, 9, 5:

   • Loading dose: 20-60 mg/kg/day (typically 1000-3000 mg IV)
   • Advantages: Fewer drug interactions, no cardiac effects, rapid administration
   • Most commonly used in survey of neurologists managing nonconvulsive seizures 5

2. Valproate 10, 9:

   • Loading dose: 15-20 mg/kg IV (can be given rapidly)
   • Advantages: Broad-spectrum efficacy, fewer acute side effects than phenytoin
   • Effective alternative to phenytoin with safer loading profile 9

3. Phenytoin/Fosphenytoin 9, 5:

   • Traditional second-line agent
   • Limitations: Hypotension, potential arrhythmias, slower administration
   • Still commonly used but increasingly replaced by levetiracetam or valproate 9, 5

Treatment of Ictal-Interictal Continuum Patterns

For EEG patterns on the ictal-interictal continuum that do not meet full criteria for seizures, a therapeutic trial of a nonsedating antiseizure medication may be reasonable (Class 2b recommendation) 1:

• The TELSTAR trial showed no clear benefit of aggressive treatment of all rhythmic/periodic patterns 1
• However, patients with unequivocal electrographic seizures (frequencies ≥2.5 Hz) or evolving patterns may benefit from treatment 1
• Use clinical judgment based on pattern characteristics and patient context 1

Refractory Nonconvulsive Status Epilepticus

If seizures persist despite first-line agents 1, 9:

• Escalate to continuous infusions: midazolam, propofol, or pentobarbital
• Consider ketamine as it is probably effective in refractory cases 9
• Maintain continuous EEG monitoring to confirm electrical seizure cessation 1, 9

Critical Pitfalls to Avoid

Do Not Withhold Treatment Based on Clinical Suspicion Alone

• Never assume pseudoseizure without EEG confirmation, as the mortality risk of untreated status epilepticus (5-65%) is too high 7
• Administer benzodiazepines immediately for any convulsive activity lasting >5 minutes, regardless of suspected etiology 7

Do Not Rely on Seizure Prophylaxis

• Seizure prophylaxis in cardiac arrest survivors is NOT recommended (Class 3: No Benefit) 1
• Only treat seizures that are actually detected, not prophylactically 1

Do Not Assume Seizure Cessation Without EEG Confirmation

• Clinical cessation of motor activity does not guarantee electrical seizure termination 7, 3
• Continue EEG monitoring for at least 24 hours after apparent seizure control 1

Do Not Delay EEG for Neurologic Consultation

• While neurologic consultation is reasonable given the specialized nature of EEG interpretation, do not delay ordering the study 2, 3
• Order EEG immediately and consult neurology concurrently 1, 2

Special Considerations

Post-Cardiac Arrest Patients

• Myoclonus occurs in approximately 20% of cardiac arrest survivors and may or may not have an EEG correlate 1
• Subcortical myoclonus without epileptiform activity may not warrant aggressive antiseizure treatment if not interfering with mechanical ventilation 1
• Distinguish between cortical myoclonus (treat) and subcortical myoclonus (may observe) using EEG 1

Resource-Limited Settings

• If continuous EEG is unavailable, perform repeated intermittent EEG recordings over 24-48 hours 1
• Simplified 6-10 electrode montages may be used when full 21-electrode montage is not feasible, though sensitivity may be reduced 1