Multiparametric Quantitative MRI Shows Enhanced Degeneration in Paramagnetic Rim Lesions and Their Perilesional Tissue in Multiple Sclerosis

Motivation: Paramagnetic rim lesions (PRLs), a subset of chronic active lesions identifiable through susceptibility-based imaging, are linked to insidious disease progression in multiple sclerosis (MS). However, data on local microstructural changes in PRLs remain limited. Goal(s): To comprehensively characterize pathological alterations within PRLs and the surrounding perilesional tissue. Approach: Employing multiparametric quantitative 3T MRI on 175 people with MS, we obtained contrasts sensitive to tissue microstructural damage. Results: PRLs exhibited more pronounced pathological alterations compared to other white matter lesions, displaying enhanced demyelination, neuro-axonal loss, and iron accumulation. Remarkably, these alterations extended into the perilesional tissue appearing normal on conventional MRI. Impact: In people with multiple sclerosis, paramagnetic rim lesions (PRLs) exhibit pronounced microstructural quantitative MRI alterations. This strengthens PRLs as reliable biomarkers for lesions with smoldering degenerative activity, and offers potential insights into their association with a more severe disease course.