Abstracts

Rationale: Focal-onset epilepsy is the most common type of epilepsy, of which 30-40% of patients are intractable. For these patients, guidelines suggest the consideration of non-pharmacotherapy options such as resective surgery and/or neurostimulation. A sizeable number of patients with refractory focal epilepsy are not amenable to resective surgery. One option for neurostimulation currently available in the United States is responsive neurostimulation (RNS), which provides closed-loop focal cortical stimulation in response to real-time electrocorticography (ECoG) activity. We describe a unique EEG finding in several patients with RNS at Vanderbilt University Medical Center (VUMC). To our knowledge this is the first documented report of RNS causing this EEG finding. Methods: We describe a case series of nine patients with RNS implantation at VUMC. During a routine post-implantation EEG on a patient with RNS, we noted a very high voltage (300-450 V), generalized spike-like discharge, lasting < 30 msec that was present in awake, drowsy and sleep states. Based on this observation, we retrospectively analyzed EEG on all nine patients after RNS implantation to determine the prevalence of this finding. Results: Our cohort (Table) consisted of five men and four women, with average age 34 years (27-50 years). Mean duration of epilepsy was 23.2 years. Seven patients had temporal lobe epilepsy and two had extratemporal foci. Six patients with temporal foci had RNS depth electrodes placed, two strip electrodes each were placed in patients with extra-temporal foci, and one patient with a dominant temporal focus had both depth and strip electrodes placed. The mean RNS current was 2.6 mA. Six patients (66%) clinically benefitted from RNS. In seven patients' EEGs, we noted a generalized, very high voltage (300-450 V), spike-like discharge, lasting < 30 msec, which was present in awake, drowsy and asleep states (Figure). There was no movement or clinical change associated with the discharges. There were no seizures during the EEG or epileptiform abnormalities preceding or following these discharges. All patients with this discharge had a temporal lobe focus while the two patients without the discharge had an extra-temporal focus. Conclusions: These results suggest that RNS implantation in temporal lobe can confer an EEG artifact caused by the RNS device. However, our cohort for extra-temporal focus is small, therefore this may not be a reliable analysis. It is important for electroencephalographers to be aware of this new artifact and future work aimed at validating our report is needed. Funding: N/A