Comparison of high-frequency oscillations detection as an epileptogenic zone biomarker using scalp and intracranial electroencephalography

INTRODUCTION: Epilepsy affects a substantial portion of the global population, with drug-resistant epilepsy (DRE) posing significant challenges. The epileptogenic zone localization is crucial for effective surgical management but remains complex with current diagnostic tools. High-frequency oscillations (HFO), specifically ripples (R) (80-250 Hz) and fast ripples (FR) (250-500 Hz), have emerged as promising biomarkers for epileptogenic zone localization, correlating with seizure-onset zones and surgical outcomes.EVIDENCE ACQUISITION: A systematic review and meta-synthesis investigation was conducted using Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidance. The inclusion criteria were cohort and observational studies comparing HFO detection using scalp and intracranial electroencephalography (EEG) in DRE patients. Bias risk was assessed using the Risk of Bias in Non-Randomized Studies of Interventions (ROBINS-I) tool. Then, GRADEPro software was employed to assess research quality.EVIDENCE SYNTHESIS: A total of 3134 articles were screened, yielding four relevant studies involving 58 patients. Scalp EEG utilized standard and high-density systems, while intracranial EEG employed grids, strips, or depth electrodes, predominantly during sleep stages. HFO detection rates varied significantly between the scalp and intracranial EEG, highlighting spatial sampling differences. Despite lower detection rates than intracranial EEG, scalp EEG reliably detected R and fast ripples (FR), suggesting its potential as a non-invasive tool for epileptogenic zone localization.CONCLUSIONS: Scalp EEG demonstrates promise in detecting HFO associated with the epileptogenic zone, particularly R.