Simultaneous scalp EEG improves seizure lateralization during unilateral intracranial EEG evaluation in temporal lobe epilepsy

Abstract

A B S T R A C TPurpose: To determine if simultaneous bilateral scalp EEG (scEEG) can accurately detect a contralateral seizure onset in patients with unilateral intracranial EEG (IEEG) implantation. Methods: We evaluated 39 seizures from 9 patients with bitemporal epilepsy who underwent simultaneous scEEG and IEEG (SSIEEG). To simulate conditions of unilateral IEEG implantation with a missed contralateral seizure onset, we analyzed the IEEG recording contralateral to the seizure onset (CL-IEEG), in conjunction with simultaneous scEEG. The following criteria were evaluated between scEEG and CL-IEEG (1) latency: the time to onset of EEG seizure (2) location: concordance of ictal onset zones and (3) pattern: congruence of EEG morphology and frequency. Results: SSIEEG correctly lateralized 36/39 (92.3%) seizures compared to 13/39 (33.3%) seizures using CL-IEEG alone (OR = 24.0, p < 0.01), 33 (84.6%) seizures using scEEG alone (OR = 2.2, p = 0.29) and 26 (66.9%) seizures using time of clinical onset alone (OR = 6.0, p = 0.01). For the three criteria evaluated, (1) 22/39 (56.4%) seizures had an earlier onset on the scEEG, compared to CL-IEEG; (2) lack of congruence of location of seizure onset was noted in 33/39 (84.6%) of the seizures; and (3) 22/39 (56.4%) seizures did not have a congruent ictal pattern. Conclusions: The chronological, topographic and morphologic features of SSIEEG can accurately detect the hemisphere of seizure onset in most cases with unilateral IEEG implantation. SSIEEG is significantly better than, IEEG, scEEG or clinical onset alone in this scenario. We propose that SSIEEG should be considered in all cases of intractable focal epilepsy undergoing unilateral IEEG evaluation.

Minimum standards for inpatient long‐term video‐electroencephalographic monitoring: A clinical practice guideline of the International League Against Epilepsy and International Federation of Clinical Neurophysiology

“…135 Scalp ictal EEG may falsely localize and lateralize focal seizures, 136 especially those arising from mesial and posterior quadrant neocortices 127,137 but may be potentially localized when iEEG is recorded. 138,139 Overall, one Class II study provides low confidence in evidence that more than one-third of patients will experience a change in management after undergoing VEM.…”

Beyond Stereo-EEG: Is It Worth Combining Stereo-EEG With Other Diagnostic Methods?

“…In the first study on 13 patients with focal epilepsy and SSIEEG, the presence of an insufficient latency, absence of congruence in the location, or lack of concordance in the EEG pattern was associated with a lower chance of detecting the seizure onset zone. In a second study, Anthony et al 14 showed that application of the same criteria can accurately detect a contralateral seizure onset in patients with unilateral iEEG implantation and simultaneous bilateral scEEG. Absence of congruence of ictal onset localization was the more sensitive feature than pattern-based or latency-based criteria and SSIEEG, when added to unilateral iEEG, provided better lateralization than the time of onset of clinical manifestations during seizures.…”

Rolling in the Deep: Surface EEG Seizures Viewed Through the Lens of Stereo EEG

“… 1 In patients with unilateral implantations, it can provide noninvasive coverage of the contralateral hemisphere, partially mitigating the risk of false seizure lateralization. 9 In patients with scalp onsets before stereo EEG onset, it raises a red flag of suboptimal implantation strategy. 4 In patients with seizures induced by potential traumatic effect during electrode implantation, it allows for comparison of their morphology with the previously recorded ictal patterns during the phase I investigation, allowing for correct identification of the patient’s habitual seizures.…”