Meta-Analysis and Case Review of Clinical, Neuroanatomical, and Electrophysiological Characteristics in Patients Undergoing Simultaneous Scalp and Intracranial EEG (SSIEEG)
Diji Johnson1, Hira Burhan1, Rajesh Sachdeo1, Rahul Guha1, Alexander Buslov1, Marina Khrizman1, Rachel Penn1, Danish Shabbar2, Arun Antony1
1Neurology, 2Neurosurgery, Jersey Shore University Medical Center
Objective:
To evaluate the utility of simultaneous scalp and intracranial EEG (SSIEEG) in the evaluation of patients with focal epilepsy.
Background:
Scalp and intracranial EEG, along with several imaging modalities, are the standard in identifying seizure onset zones in refractory epilepsy. However, the value of simultaneous scalp and intracranial EEG for localizing seizure onset is not well understood.
Design/Methods:
We conducted a PRISMA-compliant review of SSIEEG studies on PubMed, Embase, and Google Scholar from inception to September 2024. Data extracted included patient demographics, electrode placements, interictal discharge characteristics (IID), and surgical outcomes. We also present a patient with refractory focal epilepsy who underwent SSIEEG at our institution.
Results:
Eleven studies involving 238 patients, temporal lobe epilepsy (TLE, 224) and (FLE,14), were analyzed. The results related to seizure onset pattern, onset localization and lateralization, are summarized below (studies, patients). Mesial TLE showed theta/alpha ictal onsets in 75% of cases and delta onsets in 25%, challenging the belief that delta patterns are exclusive to lateral TLE(1,27). SSIEEG showed that temporal (4, 82), mesial/basal frontal (1,14) and insular (1,30) IIDs are detectable on scalp EEG and can be localized by signal processing methods like sLORETA and zero crossing patterns(1,62). SSIEEG accurately lateralized seizure onset in 92.3% of cases compared to 33% contralateral intracranial EEG (cIEEG) in patients undergoing bitemporal IEEG (1,9). Concordance in SSIEEG seizure onset features is linked to favorable surgery outcomes, while discordance may indicate incorrect seizure onset analysis (1/14).
Conclusions:
SSIEEG lateralizes and localizes the seizure onset zone, detects mesial/ basal/insural sources, identifies incorrect localization of seizure onset in intracranial EEG electrodes and predicts the outcome of epilepsy surgery. Prospective studies with larger data sets comparing IEEG and SSIEEG are needed to confirm the above findings.
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