Rationale: Some patients who initially fail epilepsy surgery may later become seizure-free, but it is unclear to what extent post-operative medical management of antiepileptic drug (AED) regimens contributes to this phenomenon, or which clinical characteristics determine the patients who receive further medical management. Methods: We performed a retrospective chart review of patients undergoing epilepsy surgery at the University of Washington Regional Epilepsy Center between 2007-2017, including patients receiving neocortical resection, temporal lobectomy, and hippocampal laser ablation. Vagal nerve stimulator (VNS) and responsive neural stimulator (RNS) procedures were excluded. We assessed seizure freedom (Engel Class I) in the preceding 12 months at “first follow-up” (330-730 days post-op) and at “last follow-up” (at least 365 days from first follow-up). We recorded details of AED changes, seizure frequency at first and last follow-up, EEG and imaging findings, and type of lesion. Fisher’s exact test and Mann-Whitney U test were used for statistical analyses. Results: Of 215 patients who underwent epilepsy surgery between 2007-2017 and had both first and last follow-up, 45.6% (98/215) were not seizure-free at the first follow-up (mean 1.1 years post-op). By the last follow-up (mean 4.7 years post-op), 20.4% (20/98) of those not initially seizure-free had become seizure-free. Within this group, there was a significantly higher portion with cavernomas (25% [5/20] vs. 1.3% [1/78] of those not seizure-free [p< 0.05]), but no other differences in clinical characteristics. Out of the 98 patients who had seizures at first follow up, 63.3% (62/98) underwent management of their AED regimens post-operatively. The rate of late seizure freedom was similar for patients with or without AED changes: 21.0% (13/62) were seizure-free at last visit with AED changes and 19.4% (7/36) without AED changes. Patients with medical management post-op had significantly higher pre-op monthly seizure rates, with a median of eight seizures per month versus four seizures per month in those with no AED changes (p< 0.05). Interestingly, there was no difference in seizure frequency during the first year post-op between patients who had further medical management (median 0.91 seizures/mo.) and those who did not (median 0.88 seizures/mo.). Patients who underwent medical management post-op also had a significantly higher proportion of post-traumatic epilepsy etiology (22.6% [14/62] vs. 2.77% [1/36] in those without AED changes [p< 0.05]); a higher rate of cortical dysplasia (12.9% [8/62] vs. 0.00% [0/36] in patients without AED changes [p< 0.05]); and a significantly lower incidence of mesial temporal sclerosis (MTS; 27.4% [17/62] vs. 58.3% [21/36] in those without AED changes [p< 0.05]). Similarly, of patients who became seizure-free with an AED change, only 7.69% (1/13) had MTS vs. 71.4% (5/7) with MTS in those who became seizure-free without AED changes (p< 0.05). There were no significant differences in which AEDs were changed between those who became seizure-free and those who did not.
Conclusions: A substantial proportion of patients who initially fail epilepsy surgery will have late seizure remission. Patients who were selected by their clinicians to undergo medical management post-operatively had a significantly higher pre-operative seizure frequency, lower occurrence of MTS, and higher rates of cortical dysplasia or post-traumatic lesions. Funding: Please list any funding that was received in support of this abstract.: No funding associated with this project.
