Authors :
Presenting Author: Claudia Mayela Torres Romero, MD – University Hospitals Cleveland Medical Center
Daniela Domínguez Peralta, MD – University Hospitals Cleveland Medical Center
Mohamed Ahmed Abdelsabour Hasan, MD – University Hospitals Cleveland Medical Center, Cleveland, OH, USA
Michael D Staudt, MD – Department of Neurological Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, USA
Neel Fotedar, MD – Epilepsy Center, Neurological Institute, University Hospitals Cleveland Medical Center, Cleveland, OH, USA
Rationale: Electrical stimulation mapping (ESM) is essential in epilepsy surgery to identify motor-eloquent cortex. While subdural grids (SDG) and stereo-electroencephalography (SEEG) are both widely used, comparative data on the characteristics of evoked motor responses by each technique are limited. This work, to our knowledge, has not been previously published or presented. We aim to fill this gap by providing a detailed comparative analysis of motor responses evoked through SDG and SEEG, highlighting stimulation thresholds, anatomical distribution, response types, and propagation patterns.
Methods: We retrospectively reviewed stimulation data from 15 patients who underwent motor mapping with SDG and 8 patients with SEEG. We analyzed each stimulation site for: (1) minimal intensity required to elicit a motor response, (2) response type (clonic or tonic), (3) anatomical distribution (tongue, face, upper/lower limb, hemibody), (4) propagation to adjacent body parts, and (5) changes in motor response with increasing current intensity. Only stimulation sites with reliable documentation and reproducible responses were included.
Results:
A total of 125 SDG and 60 SEEG electrodes, each corresponding to distinct stimulation sites, were analyzed. SEEG exhibited lower average motor thresholds (mean 4.5mA, range 2.1–9.1mA) than SDG (mean 7.8mA, range 3.5–20mA). Clonic response was the most common type of motor response elicited in both SEEG (78%) and SDG (62%) groups. SEEG elicited motor responses were mainly localized to the tongue and face, while SDG mapped wider regions including hand, arm, leg, and hemibody. Propagation to other body parts with increasing current intensity occurred more frequently in SDG (36%) than SEEG (21%), and changes in motor response pattern (clonic to tonic) with increasing intensity were observed in 41% of SDG vs. 18% of SEEG sites. Notably, negative motor responses were observed only in SDG cases.
Conclusions:
Clonic response is the most common type of motor response elicited by electrical stimulation of the primary motor cortex via SEEG and SDG both. Overall, SEEG has a lower stimulation threshold. Propagation to adjacent body parts occurs more commonly with SDG likely because the electrodes cover the surface of the pre-central gyrus and the current is more likely to spread horizontally. Negative motor responses are mostly elicited by SDG.
Funding: No funding was received for this work.