CNS B cell infiltration in tumefactive anti-myelin oligodendrocyte glycoprotein antibody-associated disease

Background Few studies have examined B cells among patients with anti-myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD), including brain pathology. Objective To describe cases of tumefactive MOGAD with B-cell dominant central nervous system (CNS) infiltration. Methods In this study, we reviewed three cases with clinical and brain histopathological features with tumefactive MOGAD. Results Forty-nine cases of tumefactive brain lesions (TBL) between January 2003 and December 2023 were included; of these, seven had MOGAD. Three underwent a brain biopsy. B-cell dominant CNS infiltration was observed in two cases. In two cases with B-cell dominant CNS infiltration, symptoms included fever, headache, nausea, somnolence, and focal neurological deficits. Cerebrospinal fluid examination revealed both mild pleocytosis and negative oligoclonal IgG bands. Magnetic resonance imaging of the brain revealed large abnormal lesions extending from the basal ganglia to the parietotemporal lobe in both cases. These cases showed a good response to steroids; however, one case relapsed. Brain pathology showed demyelination and perivascular lymphocytic infiltration. One showed small vessel vasculitis. Deposition of the activated complement component was absent or rarely observed. Loss of MOG was observed in two cases. Conclusion MOGAD could exhibit B-cell dominant CNS infiltration and small vessel vasculitis. MOGAD should be considered in differential diagnosis of TBL.