1 Montreal Neurological Institute and Hospital, McGill University, Montréal, Québec H3A 2B4, Canada. Electronic address: chifaou.abdallah@mail.mcgill.ca.
2 Montreal Neurological Institute and Hospital, McGill University, Montréal, Québec H3A 2B4, Canada.
3 Department of Neurology, Duke University Medical Center, Durham, NC, USA.
4 Montreal Neurological Institute and Hospital, McGill University, Montréal, Québec H3A 2B4, Canada; Multimodal Functional Imaging Lab, Department of Physics, Concordia University, Montréal, Québec, Canada; PERFORM Centre, Concordia University, Montréal, Québec, Canada.
5 Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark; Department of Clinical Neurophysiology, Danish Epilepsy Center, Dianalund, Denmark.
6 Department of Neurology, Duke University Medical Center, Durham, NC, USA; Department of Biomedical Engineering, Pratt School of Engineering, Durham, NC, USA. Electronic address: birgit.frauscher@duke.edu.

Objective: Increasing evidence suggests that the seizure-onset pattern (SOP) in stereo-electroencephalography (SEEG) is important for localizing the "true" seizure onset. Specifically, SOPs with low-voltage fast activity (LVFA) are associated with seizure-free outcome (Engel I). However, several classifications and various terms corresponding to the same pattern have been reported, challenging its use in clinical practice.

Method: Following the Preferred Reporting Items of Systematic reviews and Meta-Analyses (PRISMA) guideline, we performed a systematic review of studies describing SOPs along with accompanying figures depicting the reported SOP in SEEG.

Results: Of 1799 studies, 22 met the selection criteria. Among the various SOPs, we observed that the terminology for low frequency periodic spikes exhibited the most variability, whereas LVFA is the most frequently used term of this pattern. Some SOP terms were inconsistent with standard EEG terminology. Finally, there was a significant but weak association between presence of LVFA and seizure-free outcome.

Conclusion: Divergent terms were used to describe the same SOPs and some of these terms showed inconsistencies with the standard EEG terminology. Additionally, our results confirmed the link between patterns with LVFA and seizure-free outcomes. However, this association was not strong.

Significance: These results underline the need for standardization of SEEG terminology.