Abstracts

Rationale: Epilepsy affects 70 million people worldwide accounting for 1% of the overall population. 30% of these patients are drug resistant, and many of those undergo epilepsy surgery. The duration of postoperative seizure freedom varies across patients, with 50-70% remaining completely seizure-free for up to a decade after surgery, while others benefit from variable periods of seizure remission before recurrence of the epilepsy. Literature characterizing this variation in the periods of postoperative remission and their predictors is scarce, despite the fact that the period of seizure remission can have implications on lifestyle restrictions like driving and help guide post-operative medication reductions. We hypothesize that the previously validated modified seizure freedom score (m-SFS) predicts not only the binary occurrence of overall seizure freedom vs recurrence, but also the duration of seizure remission in patients who manage to achieve seizure freedom for a certain duration (1 year for this study). Methods: We studied 402 consecutive patients that underwent epilepsy surgery at the Cleveland clinic between 1995 and 2012. Data pertaining to their baseline seizure characteristics as well as details about epilepsy surgery and outcome were collected. A seizure freedom score was calculated for each of these patients per Garcia et al. Six predictive outcome indicators previously validated were selected: preoperative seizure frequency, history of generalized tonic-clonic seizures, brain magnetic resonance imaging (MRI), epilepsy duration, invasive electroencephalography (EEG) evaluation (IEI) (performed or not performed) and lobe of resection (temporal vs. extratemporal). A m-SFS was calculated by adding these six categories (total score ranged from 0 to 6). These were divided in 3 groups based on their scores with Group 1 score 0, Group 2 scores 1-3 and Group 3 scores 4-6. Statistical analysis was done using JMP statistical software.  Results: 49% of the patients were female and 35% were pediatric. 10 (2%) patients belonged to group 1, 223 (55%) to group 2 and the remaining 168 (41%) to group 3. We found that the mean interval to recurrence was shortest in patients in group 1 and increased in group 2 and 3 respectively. (P<0.0001) Fig 1. The proportion of patients who were able to achieve 1 year Sz remission after surgery in group 1 were significantly lower as compared to groups 2 and 3 (p=0.012) Fig 2A. The proportion of patients who managed to achieve 1 year seizure freedom and subsequently recurred were higher in group 1 as compared to group 2 and 3. (P=0.16). Kaplan Meier survival analysis of those patients who had already achieved a seizure freedom of one year after surgery showed that the patients in group 1 had a significantly higher chance of recurrence in comparison with those in group 2 and 3(p=0.003) Fig 2B. Conclusions: By using the seizure freedom score it is apparent that the outcome in terms of seizure remission of patients that undergo epilepsy surgery is not homogeneous. The group of patients with a lower m-SFS have a poor outcome with a shorter mean duration of seizure freedom as compared to the other groups. Additionally, even after remaining seizure free for a year the patients in group 1 have a lesser chance of remaining seizure free thereafter. Funding: No funding