Two main focal seizure patterns revealed by intracerebral electroencephalographic biomarker analysis

Long-term recording with intracerebral electrodes is commonly utilized to identify brain areas responsible for seizure generation (epileptogenic zone) and to tailor therapeutic surgical resections in patients with focal drug-resistant epilepsy. This invasive diagnostic procedure generates a wealth of data that contribute to understanding human epilepsy. We analyze intracerebral signals to identify and classify focal ictal patterns.

We retrospectively analyzed stereo-electroencephalographic (EEG) data in a cohort of patients either cryptogenic (magnetic resonance imaging negative) or presenting with noncongruent anatomoelectroclinical data. A computer-assisted method based on EEG signal analysis in frequency and space domains was applied to 467 seizures recorded in 105 patients submitted to stereo-EEG presurgical monitoring.

Two main focal seizure patterns were identified. P-type seizures, typical of neocortex, were observed in 73 patients (69.5%), lasted 22 ± 13 seconds (mean +SD), and were characterized by a sharp-onset/sharp-offset transient superimposed on low-voltage fast activity (126 ± 19 Hz). L-type seizures were observed in 43 patients (40.9%) and consistently involved mesial temporal structures; they lasted longer (93 ± 48 second), started with 116 ± 21 Hz low-voltage fast activity superimposed on a slow potential shift, and terminated with large-amplitude, periodic bursting activity. In 23 patients (21.9%), the L-type seizure was preceded by a P seizure. Spasmlike and unclassifiable EEG seizures were observed in 11.4% of cases.

The proposed computer-assisted approach revealed signal information concealed to visual inspection that contributes to identifying two principal seizure patterns typical of the neocortex and of mesial temporal networks.