Neuromyelitis optica spectrum disorder (NMOSD) is neuroinflammatory disease characterized by optic neuritis and myelitis with presence of anti-aquaporin-4 (AQP4) antibodies. Satralizumab is an anti-IL-6 receptor (IL-6R) humanized antibody approved for preventing relapses in NMOSD (AQP4 IgG positive) in adults and children in Japan.