From the Guidelines
The most common EEG findings for different seizure types include: bilateral, synchronous 3-4 Hz spike-and-wave discharges for generalized tonic-clonic seizures, 3 Hz spike-and-wave complexes for absence seizures, polyspike-and-wave discharges for myoclonic seizures, and rhythmic discharges in the temporal lobe for focal seizures with impaired awareness. When evaluating EEG findings, it's essential to consider the type of seizure and its corresponding EEG pattern. For instance:
- Generalized tonic-clonic seizures are characterized by bilateral, synchronous 3-4 Hz spike-and-wave discharges with high amplitude 1.
- Absence seizures show 3 Hz spike-and-wave complexes with abrupt onset and termination.
- Myoclonic seizures display polyspike-and-wave discharges or irregular spike-wave complexes.
- Atonic seizures are associated with diffuse polyspikes followed by attenuation of background activity.
- Focal seizures with impaired awareness (complex partial) demonstrate rhythmic discharges in the temporal lobe, often with 4-7 Hz theta activity.
- Simple focal seizures show localized spikes or sharp waves in the affected cortical region.
- Infantile spasms present with hypsarrhythmia, a chaotic high-voltage pattern with multifocal spikes.
- Status epilepticus is characterized by continuous seizure activity lasting more than 5 minutes or recurrent seizures without recovery between them.
- Lennox-Gastaut syndrome displays slow spike-and-wave complexes at 1.5-2.5 Hz.
- Juvenile myoclonic epilepsy shows 4-6 Hz polyspike-and-wave discharges, particularly during photic stimulation 1. Understanding these patterns is crucial for accurate diagnosis and appropriate treatment selection in epilepsy management, as emphasized in the 2024 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations 1.
From the Research
EEG Findings in Seizure Disorders
The following are common EEG findings corresponding to each type of seizure:
- Generalized Tonic-Clonic Seizures: characterized by generalized spike or polyspike and slow-wave discharges on EEG, often preceded by a period of impaired awareness 2
- Absence Seizures: typically show generalized spike and wave discharges on EEG, often with a frequency of 3 Hz 2
- Myoclonic-Atonic Seizures: may exhibit generalized polyspike and wave discharges, as well as atonic seizures with a brief loss of muscle tone 3
- Idiopathic Generalized Epilepsies: often characterized by generalized spike and wave discharges, as well as polyspike and wave discharges on EEG 2, 3
- Focal Seizures: may show focal spikes or sharp waves on EEG, indicating a localized area of abnormal brain activity 4
Interictal and Ictal EEG Findings
Interictal EEG findings, such as spikes and sharp waves, can support the diagnosis of epilepsy when a habitual seizure is not captured by EEG 4. Ictal EEG findings, on the other hand, can help confirm and classify seizure disorders 4, 2.
EEG Monitoring in Seizure Diagnosis and Treatment
Continuous critical care EEG monitoring is essential in the diagnosis and treatment of subclinical seizures and nonconvulsive status epilepticus 4, 5. Intracranial EEG monitoring with subdural or intraparenchymal electrodes can help localize the seizure focus and map eloquent brain areas for epilepsy surgery 4.