Leptomeningeal Contrast Enhancement Is Related to Focal Cortical Thinning in Relapsing-Remitting Multiple Sclerosis: A Cross-Sectional MRI Study

BACKGROUND AND PURPOSE: Leptomeningeal inflammation is associated with the development of global cortical gray matter atrophy in multiple sclerosis. However, its association with localized loss of tissue remains unclear. The purpose of this study was to evaluate the relationship between leptomeningeal contrast enhancement, a putative marker of leptomeningeal inflammation, and focal cortical thinning in MS. MATERIALS AND METHODS: Forty-three patients with relapsing-remitting MS and 15 with secondary-progressive MS were imaged on a 3T scanner. Cortical reconstruction was performed with FreeSurfer. Leptomeningeal contrast-enhancement foci were visually identified on 3D-FLAIR postcontrast images and confirmed using subtraction imaging. Leptomeningeal contrast-enhancement foci were mapped onto the cortex, and ROIs were obtained by dilating along the surface multiple times (n = 5, 10, 15, 20, 25, 30, 35, 40). Resulting ROIs were then mapped onto the homologous region of the contralateral hemisphere. Paired t tests compared the thickness of the cortex surrounding individual leptomeningeal contrast-enhancement foci and the corresponding contralateral region. Results were corrected for the false discovery rate. RESULTS: Differences between ipsilateral and contralateral ROIs progressively decreased with larger ROIs, but no significant effects were detected when considering the entire MS sample. In patients with relapsing-remitting MS only, significantly reduced cortical thickness was found for 5 dilations (-8.53%, corrected P = .04) and 10 dilations (-5.20%, corrected P = .044). CONCLUSIONS: Focal leptomeningeal contrast enhancement is associated with reduced thickness of the surrounding cortex in patients with relapsing-remitting MS, but not in those with secondary-progressive MS. Our results suggest that pathology associated with the presence of leptomeningeal contrast-enhancement foci has a stronger, localized effect on cortical tissue loss earlier in the disease.