S133. How Fragile is the Left Hemisphere? VBM Analyses Comparing Epilepsy, Amyotrophic Lateral Sclerosis and Parkinson’s Disease

Differences between left and right hemispheres regarding susceptibility to disease process is not entirely clear. In Temporal lobe epilepsy (TLE), left hippocampal sclerosis (HS; LTLE) is associated with bilateral structural damage, while in right HS (RTLE) there is more ipsilateral pattern of abnormalities. The reasons for such differences are unclear. Here we investigate the impact of neurodegenerative diseases [Amyotrophic Lateral Sclerosis (ALS) and Parkinson Disease (PD)] on patterns of structural grey matter alterations, comparing abnormalities on left and right hemispheres. We performed Voxel Based Morphometry analyses on T1 weighted images with MATLAB2014b/SPM12, comparing patients and paired controls (age and gender) for each separate disease. We included 99 patients with ALS, 113 patients with PD, 45 with RTLE and 50 with LTLE and 265 healthy controls. Basically, images were segmented into grey and white matter individual maps, modulated and smoothed. Posteriorly, we performed T-tests for ALS and PD, and a full factorial model for RTLE/LTLE. All statistical analyses were performed on SPM12. As expected, we observed a more bilateral pattern of GM atrophy on LTLE, while RTLE present more ipsilateral GM atrophy. Interestingly, the analysis of other neurodegenerative diseases (which are not usually associated with specific MRI lesions such as hippocampal sclerosis) revealed a more left sided pattern of GM atrophy for both ALS and PD. The results show an intriguing pattern of GM alterations on both ALS and PD, as visual analysis is usually unremarkable and mostly because neurological deficits are usually bilateral, especially at late stages. On TLE we speculate that left HS causes more widespread damage probably because left hemisphere is highly connected with right hemisphere, with more unidirectional pathways. The present work suggests that left hemisphere is somehow more susceptible to damage, regardless to the pathogenic process (i.e. seizures, neurodegeneration). Further analyses including hand dominance as covariate may help us to understand better these left/right side differences.