A quadruple examination of ictal EEG patterns in mesial temporal lobe epilepsy with hippocampal sclerosis: onset, propagation, later significant pattern, and termination.

PURPOSE

The purpose of this study was to analyze electrophysiological properties of four main stages of ictal patterns of patients with operated temporal lobe epilepsy related to hippocampal sclerosis.

METHODS

We included 48 patients with temporal lobe epilepsy-hippocampal sclerosis. Seizures were classified according to their electrophysiological properties and surgical outcomes as seizure-free and not seizure-free. The EEGs with artifacts at the beginning were analyzed separately.

RESULTS

The most frequent type of ictal onset patterns was rhythmic theta/alpha activity, which was correlated to seizure-free group, whereas "switch of lateralization" and "bitemporal asynchrony" correlated to not seizure-free group. When bilateral independent ictal propagation patterns emerged, seizures tended to predict the side of epileptogenic zone wrongly. As a later significant pattern, rhythmic theta/alpha activity lateralized the focus correctly. Seizure termination was significantly concordant with hippocampal sclerosis lateralization in the seizure-free group.

CONCLUSION

Ictal onset pattern with rhythmic theta/alpha activity correlates well with seizure freedom. Morphology of later significant patterns was more important in determining the lateralization reliability than time of appearance. The EEGs with short artifacts at the beginning are seen to be valuable in presurgical evaluation. Lateralization of ictal termination ipsilateral to MRI indicates good prognosis after surgery. Scalp EEG monitoring helps predict epileptogenic zones and postsurgical outcomes.