Focal evolution following apparent interictal period on scalp electroencephalography in generalized epilepsy: a three-case study.

PURPOSE: To classify epilepsy type in patients exhibiting focal evolution following a brief interval immediately after a generalized spike-and-wave complex (GSWC) on scalp video EEG (vEEG) monitoring.

METHODS

We retrospectively reviewed 389 patients aged 18 or older who underwent vEEG between January 2020 and January 2025. Ictal EEG was categorized into Phase I (GSWC), Phase II (short-lasting abnormal bilateral background EEG activity), and Phase III (focal evolution).

RESULTS

Five ictal recordings from three patients (median age, 24 years, range: 20-26 years) were identified. All patients had normal cognition, no family history of epilepsy, and no myoclonus. Bilateral tonic-clonic seizures occurred in all, sometimes preceded by behavioral arrest or unilateral head rotation. EEG showed symmetrical GSWC (2-6 Hz, 2.5-7.6 s) in Phase I, bilateral abnormal background activity without epileptiform discharges in Phase II (0-21 s), and focal EEG evolution consistent with clinical signs in Phase III. This pattern was reproducible in two cases. Interictal EEG showed symmetrical GSWC (2-6 Hz). Background EEG activity was normal in all cases, and magnetic resonance imaging revealed no significant structural abnormalities. The interictal EEG findings and consistent focal evolution pattern following GSWC, along with the associated clinical manifestations, suggest that these three patients have genetic generalized epilepsy rather than focal epilepsy. Treatment with sodium valproate and lamotrigine was effective.

CONCLUSION

In the seizure pattern of focal evolution in generalized epilepsy, an apparent interictal period may occasionally appear on scalp EEG before focal evolution, which warrants careful consideration in diagnostic interpretation.