Investigation of in-vivo GABA⁺ and Glutamate levels in patients with drug resistant unilateral temporal lobe epilepsy using MEGA-PRESS and correlates with clinical semiology

Background: In this study, we used in vivo MEGA-PRESS spectroscopy to investigate GABA and Glu levels in patients with drug-resistant unilateral temporal lobe epilepsy (TLE) and also look for correlation between neurometabolites and clinical semiology assessed by other modalities. Materials and methods: Twenty-five patients with TLE underwent MRS data acquisition on a 3.0 T MRI. Bilateral single-voxel MEGA-PRESS data was acquired from mesial temporal lobes, and data was post-processed using MRSpa and LC-Model for computing neurometabolites concentration. Tissue segmentation from spectroscopic voxel was performed for tissue metabolite and CSF correction. Statistical analysis was performed to analyze differences in neurometabolic between affected and normal-sides and clinical correlations. Results: GABA, Glu, NAA, Cr, and Cho neurometabolites were computed. The group-wise statistical comparison revealed a significantly reduced NAA level from the affected compared to normal-side of the hippocampus (p-value=0.039). We observed reduced GABA (p-value=0.07) values and hippocampal volume (p-value<0.001) were observed from the affected side. A significant negative correlation was noted between affected-side hippocampal volume and NAA concentration (rho=-0.497, p-value=0.05). Glu/NAA ratios from both affected (rho=-0.692, p-value=0.012) and normal-sides (rho=-0.608, p-value=0.016) of the hippocampus were negatively correlated with age. Concordance between neurometabolites with video-EEG for lateralization demonstrates correct classification percentage for GABA was 86.7 %, indicating that there is an 86.7 % chance that GABA will be able to lateralize the unaffected side as detected by VEEG. Conclusion: A novel exploratory study demonstrates an alternation of in-vivo GABA and Glu levels and hippocampal volume. This study may provide a direction for utilizing MEGA-PRES as a presurgical tool for assessing in-vivo neurometabolic profiles and add to the knowledge of the role of GABA and Glu in epilepsy and its interplay.