Abstracts

Rationale: Direct electrical stimulation (DES) is primarily used for functional mapping. When DES is used for seizure induction, it is often done selectively. The primary aim of this study was to prospectively investigate the utility of systematic DES for reliably identifying the seizure onset zone (SOZ), explore concordance with spontaneous SOZ, and its relation to surgical outcome.

Methods: Prospective cohort study of consecutive patients with focal drug-resistant epilepsy who underwent intracranial EEG (icEEG) between 2018 and 2021. All patients underwent systematic 1 Hz DES for seizure induction. All or most of the gray matter contacts were stimulated at an amperage of 1 mA, 5 mA, and 10 mA for 30 to 60 sec at each amperage. Stimulation was bipolar, biphasic, and with a pulse width of 0.3 msec. A select group of the patients in this cohort also underwent 50 Hz stimulation for seizure induction. All patients had at least one-year surgical outcomes. Variables were analyzed using the Fisher’s exact test, the Χ2test, or the Mann-Whitney test, as appropriate.

Results: Forty-one patients were included in the study cohort. _x000D_
1 Hz stimulation results: All 41 patients underwent 1 Hz stimulation. Fifty-six percent (23/41) of patients had seizures induced with 1 Hz, and 83% (19/23) were habitual. Table 1 shows the electroclinical characteristics of these patients. Presence of an aura and a focal icEEG onset pattern increased the odds of stimulating a habitual seizure with 1 Hz. Sixteen patients in this cohort underwent a resective surgery after DES. Eleven of 16 in this subgroup had habitual seizures induced with 1 Hz, all of whom had that area resected, and all 11 patients had a good outcome (ILAE class I or II) at one year follow up (P< 0.0001), while the remaining five patients (no seizures induced with 1 Hz) had a poor outcome (ILAE class III or IV). _x000D_  _x000D_ 50 Hz vs 1 Hz results