Ictal scalp EEG patterns are shaped by seizure etiology in temporal lobe epilepsy

Objective To investigate how etiology and seizure localization influence ictal scalp electroencephalographic (EEG) patterns in temporal lobe epilepsy (TLE). Methods We retrospectively analyzed ictal EEG features from 504 focal seizures recorded in 189 TLE patients with various etiologies who underwent resective surgery. Results For seizure onset patterns (SOPs), alpha/beta onset was more common in the low-grade tumor group (38.4%) than in the hippocampal sclerosis (HS) group (14.1%, p < 0.001). The ictal EEG duration was shorter in the tumor group compared to the focal cortical dysplasia (FCD), HS, and non-specific groups (p < 0.05). Among mesial TLE patients, SOPs varied depending on the etiology. Within both the tumor and non-specific groups, SOPs and the spreading time to the contralateral hemisphere differed between mesial and neocortical origins. Ictal pattern (87.7%) and ictal theta activity (83.9%) correctly lateralized the seizure in most cases. Significance The ictal scalp pattern in TLE is influenced by both etiology and seizure localization. TLE associated with low-grade tumors exhibits distinct ictal EEG characteristics. Furthermore, ictal pattern and ictal theta activity are equally effective in lateralizing seizures, regardless of etiology. Plain Language SummaryThis research examined how brain activity during seizures in people with temporal lobe epilepsy can be different based on what caused the epilepsy and where in the brain the seizure starts. We found that seizures caused by brain tumors have unique patterns in the brain's electrical activity. Additionally, we discovered that specific patterns and types of brain waves can help determine which side of the brain the seizure is occurring on, regardless of its cause.