Neuromyelitis Optica Spectrum Disorder: Clinical Features and Treatments Revisited

ABSTRACT Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease of the central nervous system, characterized by severe relapses that can lead to blindness or paralysis. However, NMOSD presents with a broad spectrum of symptoms, including optic neuritis, transverse myelitis, and area postrema syndrome, along with distinctive findings on magnetic resonance imaging. In Japan, where the prevalence of NMOSD is relatively high, nationwide surveys and regional studies have revealed its detailed epidemiological and clinical characteristics. The discovery of aquaporin‐4 autoantibodies has not only distinguished NMOSD from multiple sclerosis but also provided critical insights into its immunopathogenesis, resulting in the development of molecular‐targeted therapies capable of inhibiting key immune pathways, including the complement system, interleukin‐6 signaling, and B‐cell‐mediated immunity. Several biological agents, such as eculizumab, ravulizumab, satralizumab, inebilizumab, and rituximab, have demonstrated high efficacy in preventing relapse in clinical trials. Although long‐term safety data remain limited for most agents, Japanese real‐world data support their effectiveness and safety. This review summarizes the clinical features, imaging characteristics, and current treatment strategies for NMOSD, with a particular focus on the therapeutic mechanisms of biological agents and the insights they provide into disease pathophysiology.