Identification of Drug-Resistant Laterality in Bilateral Temporal Lobe Epilepsy

Selecting the optimal resection side in bilateral temporal lobe epilepsy (BTLE) remains a challenge due to independent seizure origins in both temporal lobes. This study, therefore, aimed to evaluate whether antiseizure medication (ASM)-induced changes in the Modulation Index (MI), a measure of phase-amplitude coupling, could serve as a biomarker for determining the predominant laterality of drug resistance in BTLE. A 35-year-old patient with drug-resistant BTLE underwent stereoelectroencephalography (SEEG) targeting bilateral temporal structures. To assess refractory epileptic focus, MI values were compared between the ASM-withdrawn and ASM-resumed states. The MI was calculated between high-frequency oscillations and 3-4 Hz slow-wave activity during interictal epochs. Following ASM resumption, MI values significantly decreased in the right hippocampus and entorhinal cortex, while the left entorhinal cortex showed persistently elevated MI without significant reduction. These findings indicated a more refractory epileptic focus in the left temporal lobe. A left temporal lobectomy was performed, leading to seizure freedom for 37 months (International League Against Epilepsy (ILAE) Class 1), without changes in the ASM regimen. ASM-induced MI changes in interictal SEEG may offer insights into lateralizing the more refractory temporal lobe in patients with BTLE and could potentially support resection side selection. However, further studies in larger cohorts are warranted to confirm its clinical utility and to establish standardized MI thresholds.