Registry of Patients With AQP4+ NMOSD Treated With Alexion C5 Inhibitor Therapies

Inclusion Criteria: * Participant is ≥ 18 years of age at the time of enrollment in the Registry. * Participant must have a confirmed diagnosis of AQP4+ NMOSD. * At the time of enrollment in the Registry, participants must be receiving treatment with ALXN-C5IT for the purpose of chronic relapse prevention in a manner consistent with the local label. Specifically, they should have received at least 1 dose of eculizumab within 4 weeks prior to enrollment or at least 1 dose of ravulizumab within 12 weeks prior to enrollment. * Participants must have both the following historical data available to be enrolled in the Registry: ALXN-C5IT dosing information since initiation and number and types of relapses from 1 year prior to ALXN-C5IT initiation through Registry enrollment. Exclusion Criteria: * Participants currently enrolled in an interventional clinical study for the treatment of AQP4+ NMOSD in which the intervention is a drug.