S11. EEG source localization of interictal discharges and outcome for LITT for temporal lobe epilepsy

Abstract

Introduction Approximately one-third of patients with epilepsy are intractable to antiepileptic drug therapy. In patients with intractable focal epilepsy, resection or ablation of the seizure focus offers a chance for seizure control. Laser interstitial thermal therapy (LITT) is one type of epilepsy surgery used to ablate the ictal zone. For patients with a presumed mesial temporal lobe focus, this technique can be used to ablate the hippocampus and nearby mesial structures. Seizure outcomes are similar to open surgery, although data is limited. It would be helpful to have factors that can be used to predict who will have a good outcome with LITT versus who might be better served by an open procedure. The precise location of interictal epileptiform discharges (as determined from scalp EEG data and EEG source image, ESI) may be one such factor.We plan to present a case series of 16 patients who underwent LITT for intractable temporal lobe epilepsy at our institution. We hypothesize that patients will have a good outcome if the location of the ESI-determined interictal epileptiform discharge is present within the area of ablation. Methods In this retrospective case series, subjects were identified using epilepsy center logs. Patients were included if they underwent pre-operative scalp EEG and high-resolution MRI, LITT, postoperative MRI and had a follow-up appointment. Patient’s scalp EEG and high-resolution MRI were used to determine the location of the interictal discharge using commercially available software (Curry Neuroimaging Suite, Compumedics, Inc). We then compared the result to post-ablation MRI. The clinical outcomes were determined from the patient’s chart at the follow-up appointment. Results Using ESI, we modeled the interictal discharges for two patients. Both patients’ scalp EEG showed temporal lobe onset for seizures and interictal discharges. Both underwent LITT of the left mesial temporal lobe. The first patient has been seizure free for one year (Engel 1). ESI suggested a source for interictal epileptiform discharges to be mesial temporal lobe which was included in ablated area as depicted by the post-ablation MRI. The second patient continues to have seizures at her follow-up appointments, although less frequently than before (Engel 2). ESI suggested left lateral temporal lobe interictal epileptiform discharges, which were not included in the ablated area as depicted by post ablation MRI.We ultimately plan to model all 16 patients. Conclusion Our preliminary results suggest that patient whose source of the interictal epileptiform discharges was located in the ablated volume have a good outcome. We plan to test this conclusion against a broader data to see if this method can be used to predict which patients are likely to have a good outcome.