MOG and myelitis: In a retrospective multicenter study of MOG-IgG-seropositive NMOSD patients, 88% of the patients developed acute ON at least once, 56% of the patients developed acute myelitis at least once, 44% of the patients only had a history of ON but not of myelitis, while only 12% of the patients had a history of myelitis but not of ON (29).