Abstracts

Rationale:
The last twenty years brought significant change to the way epilepsy patients are referred, evaluated and treated. Novel pre-operative imaging and neuropsychological tests, changing trends in intracranial electroencephalography (icEEG) techniques and the introduction of neuromodulation have ushered in a paradigm shift that now frequently describes focal epilepsy as a network disorder. In the current study, we evaluate twenty years of epilepsy surgery from Yale and the literature to describe how the approach to focal epilepsy has evolved.
Method:
We reviewed 201 consecutive patients with at least 1-year follow-up who underwent icEEG evaluation at the Yale Comprehensive Epilepsy Program in five-year epochs from 2000 to 2019. Similarly, we reviewed 129 manuscripts published between 2000 and 2020 in five-year epochs. Information about pre-surgical workup, icEEG procedure, outcomes and complications were described in both cohorts.  
Results:
The majority of papers originated from the US (42%) and Europe (36%) with representation from the rest of the world increasing over time. Each paper reported an average of 50 patients per 5-year time period. Similarly, 50 patients underwent an intracranial study at Yale every 5-years. Overall, 67% of patients were MRI-positive at Yale compared to 58% in the literature. There was a 70% reported chance of seizure regionalization on scalp EEG in the literature and at Yale. Despite this, there was a clear increase in the reporting of preoperative PET, MEG and neuropsychological testing, reflecting increased desire for corroborating scalp data prior to intracranial study. SPECT reports increased until 2015 when it began to decline. Stereo-electroencephalography (SEEG) originated and gained favor in Europe over 20 years while the majority of subdural (SDE) and combined depth and subdural (CicEEG) studies were described in the US. As SEEG increased in major US centers in 2010, a steady rise of SEEG literature emerged, with the US representing 25% of the literature this past decade. At Yale, CicEEG monitoring was mostly performed since the year 2000, with a steady increase in the total number of contacts used. In 2015 we began using SEEG for survey studies, representing 35% of icEEG and an attendant drop-off in the number of intracranial contacts used. Both at Yale and in the literature, approximately 80% of patients went on to a definitive surgical intervention from icEEG. As previously described, there was a decline in the number of reported medial temporal lobectomies from 2000 to 2020. In 2005 neuromodulation became available at Yale, with a steady rise in these cases and a decrease in the fraction of non-operative cases. Neuromodulation represents 33% of definitive surgical intervention since 2015. Overall, approximately 70% of patients achieved seizure freedom (Engel 1 and 2) at most recent follow-up in the literature and at Yale.
Conclusion:
Despite significant advances in preoperative seizure localization and evolving technical methods for electrode placement there have been no reported improvements in seizure freedom rates in the literature since the year 2000. We believe this unfortunate trend represents a mischaracterization of focal epilepsy as emerging from one epileptogenic site and if this region is not revealed, a trend toward palliation. Research from intracranial studies has only recently begun to elucidate seizure networks and their relation to outcomes. In order to avoid complacency regarding our outcomes, we believe we must tailor icEEG studies toward individual patients with the goal of understanding focal epileptic networks and driving research forward. Furthermore, we must continue to view epilepsy as a curable disease and not allow new palliative therapies to drive us off course. 
Funding:
:NA