Abstracts

Rationale: Intracranial monitoring is a frequent component of presurgical evaluation for medically refractory epilepsy. There are several published reports of improved seizure control in patients following removal of implanted electrodes who did not proceed to surgical resection. We sought to review the cases at the Wake Forest Comprehensive Epilepsy Center that had invasive electrodes but did not have resective surgery, in order to determine how commonly we encountered this phenomenon and whether the effects persisted long term. Methods: We retrospectively reviewed the past 80 cases of intracranial monitoring for medically refractory epilepsy at our center through May 2014. 23 of these patients (29%) did not proceed to epilepsy surgery. We reviewed charts to determine placement of intracranial electrodes, number of seizures captured in epilepsy monitoring unit (EMU) admission, seizure control compared to baseline after electrode placement, as well as duration of followup. For those patients with improved seizure control we noted whether there were significant changes in treatment regimens following electrode implantation which may have played a role in reducing seizures. Results: Three patients had no seizures during invasive EMU admission, all of whom have maintained a lower than baseline seizure frequency following explantation. An additional four patients, who had multiple seizures during admission, with poor or bilateral localization, also had improved seizure control after explantation. Four of the 23 patients (17%) were seizure free for at least 6 months following electrode removal, with the longest seizure free interval of 27 months, and longest documented improvement was 47 months. Five patients were lost to followup so no determination of subsequent seizure frequency could be made. Three patients who did not have initial seizure improvement went on to have vagal nerve stimulator and one patient had a deep brain stimulator implanted. Conclusions: Medically refractory epilepsy patients occasionally will have unsuccessful invasive monitoring in the EMU recording no seizures, or an inadequate number of seizures, so that surgery cannot be recommended. Nonetheless, a small proportion of these patients will have significant improvement in seizure control despite the fact that the only intervention was the electrode implantation. Interestingly, the patients who had the least productive invasive EMU admissions were all free of seizures for at least 1 month after discharge. This series may suggest that acute reduction in seizure frequency at the time of electrode implantation may predict at least a short term remission of seizures after their removal, and possibly long term improvement in overall seizure control. We conclude that this phenomenon is infrequent and transient, although certainly fortuitous for those patients.