However, the frequency of simultaneous myelitis and ON at disease onset, i.e., as the initial presentation, was much higher in MOG-IgG-positive patients (23 % of all patients with a history of ON and myelitis) than in AQP4-IgG-positive NMOSD patients (6.7 % according to [34]; p < 0.03). Here, AQP4 is linked to myelitis.