Quantifying the Impact of Ocrelizumab on Paramagnetic Rim Lesions in Multiple Sclerosis

Paramagnetic rim lesions (PRLs) are a subset of chronic active multiple sclerosis (MS) lesions marked by iron-laden microglia and macrophages. Ocrelizumab, a monoclonal antibody targeting CD20+ B cells, suppresses acute MS activity, but its effect on PRLs remains unclear. In a longitudinal study of 29 ocrelizumab-treated patients with at least one PRL on quantitative susceptibility mapping (QSM), 97 PRLs were identified. Before treatment, PRLs showed higher QSM values than non-PRLs (p = 0.001), indicating iron enrichment. After treatment, PRLs demonstrated a greater QSM reduction (p < 0.001), with an accelerated decline in susceptibility. These findings suggest ocrelizumab may attenuate iron-related inflammation in PRLs.