Abstracts

Rationale: Epilepsy surgery is an effective treatment option in patients with medically refractory focal epilepsy, rendering about 50-70% of them seizure free. A small proportion who don’t benefit from a first surgery, may be re-evaluated for another resection. Little is known about how seizure outcomes or their predictors vary with re-operation. Methods: This is a retrospective study of 895 patients that underwent epilepsy surgery at the Cleveland Clinic from 1995 to 2016. Patients that underwent a single epilepsy surgery served as controls and were compared to those that had more than one surgery. Baseline characteristics and known predictors of seizure outcome were recorded, analyzed and adjusted for, to create comparable groups (Table 1). Detailed information pertaining to particulars of surgery, pathology and post-operative seizure recurrence was collected for each patient. Statistical analyses were performed to explore differences in outcomes and outcome predictors between the groups using SAS Software. Results: 883 patients were studied (12 records were removed due to incomplete information). 50% were female, a third of them were pediatric patients and 68% had temporal resections while the rest were extra-temporal. 801 patients had one epilepsy surgery, 69 had 2 surgeries and 13 had more than 2 surgeries. Among the patients with one surgery 49% remained seizure free at follow up as compared to 38% with 2 epilepsy surgeries and 31% with more than 2, hazard ratio 1.38 (95% CI: 1.01, 1.89; p=0.034). Patients who underwent more than one surgery were more likely to have an Engel score greater than 1 (p < 0.001) (Figure 1). On analyzing predictors of surgical outcome among patients who had multiple surgeries (N=82), 18% of patients with a normal initial MRI were seizure free as compared to 40% of those with an abnormal initial MRI (p=0.07). Of the patients who underwent an invasive evaluation with intracranial electrodes prior to the surgery, 22% attained seizure freedom, while 49% who had no invasive monitoring were seizure free (p=0.03). 24% remained free of seizures when the pathology was found to be malformations of cortical development (MCD), 31% with mesial temporal sclerosis (MTS), 38% with non specific gliosis and 55% with all other pathologies(p=0.69). If pathology was consistent across all the surgeries 45% were seizure free and when the pathology differed after subsequent surgeries, 35% achieved seizure freedom (p=0.23). Conclusions: With every subsequent epilepsy surgery, there is a lower chance of attaining seizure freedom and possibly a tendency towards surgical refractoriness. Multiple surgeries correlate with higher Engel scores, and persistence of more disabling seizures. Amongst variables altering the outcomes, re-operations in patients with a lesional MRI correlated with a good outcome while the patients with prior invasive EEG monitoring had a poor outcome, both probably indicating a difficult to localize epileptogenic zone. These results might be helpful in the selection of candidates for repeat surgery in patients with intractable focal epilepsy. Funding: None