Abstracts

Rationale: Use of stereoelectroencephalography (SEEG) is increasingly common (Rolston et al. 2014) as an alternative to subdural grid and strip arrays in invasive epilepsy surgery workups. A widely held perception of SEEG is the apparent lack of biologic artifacts to which scalp EEG is susceptible. Infrequently, however, EMG artifacts are recorded from SEEG electrodes and their amplitude and frequency signature may mimic high frequency oscillations (HFOs), which have been demonstrated to be of high localizing value regarding the epileptogenic zone (Kovac et al. 2016). Methods: We present two cases of patients with drug-resistant focal epilepsy who underwent stereoelectroencephalography (SEEG). Bihemispheric implantation with multi-contact electrodes was performed. Locations of the SEEG electrodes were coregistered with MRI imaging to ensure proper surgical placement. Results: Interictal SEEG demonstrated periodic bursts of low amplitude fast activity and variable high frequency (30-80Hz) activity (Gotman 2009). This affected proximal/superficial orthogonally introduced electrodes in close proximity to temporalis and masseter muscles. Time locking the bursts to chewing on video analysis verified the source of the burst activity as EMG artifact. Conclusions: Based on proximity to muscles of mastication, SEEG electrodes may demonstrate EMG artifact. Presumed signal attenuation by the skull may attenuate amplitude of this artifact and mimic both the frequency and amplitude characteristics of pathologic HFO activity. Multiple band frequency analysis (Otsubo et al. 2008) has been suggested as a quantitative method to distinguish these phenomena. We suggest that knowledge of electrode position and coordinated viewing with accompanying video may suffice to identify this infrequently encountered artifact. Funding: No funding