Abstracts

Rationale: The T1/T2 ratio has been proposed as a semi-quantitative measure of myelin density and is part of the Human Connectome imaging pipeline (Glasser et al 2014 Neuroimage).While there are several studies examining cortical atrophy and changes in DTI measures (e.g. fractional anisotropy and mean diffusivity) in TLE, Cortical myelin density, to our knowledge, has not been studied (Imamura et al 2016 Epilepsy Res, McDonald et al 2016 Epilepsia). In this study we investigate if reduction in myelin density is present in patients with temporal lobe epilepsy(TLE) and its correlation with cortical thinning. Methods: Study participants included 38 TLE subjects and 38 controls recruited from the Medical College of Wisconsin and the University of Wisconsin as part of the ongoing Epilepsy Connectome Project(ECP). All subjects were between the ages of 18-60 and epilepsy participants had a clinical-electrographic diagnosis of TLE with no overt structural abnormalities on MRI other than mesiotemporal sclerosis. The  3T connectome MRI protocol was used for all participants. The data were processed through the human connectome imaging pipeline (Glasser et al 2013 Neuroimage). We used a regional analysis of mean bias corrected T1/T2 ratio (FIGURE 1) and mean cortical thickness for the FreeSurfer Desikan-Killiany parcellation. The difference between control and TLE subjects was assessed using permutation testing of means for myelin density using the “coin” package and using a linear model correcting for age for cortical thickness using the “nmle” package performed in R (R Core Team Vienna, Austria). An alpha level was set at 0.05 and corrected to a 5% false discovery rate using the Benjamini-Hochberg method.  The regional correlations between myelin density and cortical thickness in TLE subjects was calculated using Pearson’s coefficient. Results: The regions of significant difference between TLE subjects and controls were in expected regions for both myelin density and cortical thickness though the correlation between these areas was only marginal and in most cases negative (Table 1). There was only one region of significant difference in the myelin density, the left parahippocampal gyrus, while the changes in cortical thickness were more widespread. Conclusions: These findings suggest that myelin density provides information independent of cortical thickness, though the degree of differences between TLE patients and controls may be subtle. More study with a larger sample size is needed.   Funding: NIH U01 Epilepsy Connectome Project: 1U01NS093650-01