Characterizing Paramagnetic Rim Lesions in Relapsing-Remitting Multiple Sclerosis: A Study on Myelin Content and Axonal Density

Motivation: The impact of paramagnetic rim lesions (PRL) and black hole lesions (BH) on physiopathology and clinical outcomes in relapsing-remitting multiple sclerosis (RRMS) patients is not well understood. Goal(s): To assess myelin and axonal content in PRL and BH coexisting lesions and their clinical significance in RRMS patients. Approach: Neurite density index (NDI) and Susceptibility Source Separation (SSS) maps were used to compare myelin and axonal content across PRL+BH+, PRL+BH-, PRL-BH+, and PRL-BH- lesions. Results: PRL+BH+ lesions showed the lowest myelin and axonal content and were most strongly associated with cognitive and physical disability, highlighting their greater clinical relevance. Impact: PRL+BH+ is a more destructive subset of PRL associated with disability in RRMS. Preventing PRL+BH- from converting to PRL+BH+ may help slow disability progression. This imaging feature also provides a novel outcome variable for clinical cohort studies.