AMAZE

Treatment tested

• Ravulizumab

  Complement C5 inhibitor

Inclusion Criteria: 1. Signed informed consent available prior to conduct of any study associated activities 2. Men and women > 18 years of age 3. Aquaporin-4 IgG positive people with neuromyelitis optica spectrum disorder treated with commercially available ravulizumab in a manner consistent with the approved indication 4. Expanded Disability Status Scale score of \<7.0 Exclusion Criteria: 1. Individuals who are intolerant to MRI 2. Individuals previously exposed to eculizumab with treatment discontinuation due to lack of effective disease control (i.e., clinical relapse or demonstration of MRI advancement after 12 weeks of sustained treatment exposure) 3. Unresolved meningococcal disease 4. History of an active infection 5. Existing participation in neuromyelitis optical spectrum disorder interventional clinical studies 6. Pregnant or lactating women

This is an observational study to: * evaluate the on-treatment clinical performance of ravulizumab in relation to the pre-treatment time period (time period prior to exposure), * enhance knowledge regarding conventional MRI outcomes in people with NMOSD treated with ravulizumab, * identify factors suggestive of subclinical disease progression through conventional MRI sequences, * determine if treatment with ravulizumab, impacts longitudinal 3D conformational MRI measures at the dorsal medulla and other regions of the CNS, and * identify biomarkers (e.g., serum neurofilament light chain (sNfL), conventional and novel MRI markers, etc.) related to disease activity.