Neuromyelitis optica (NMO), formerly known as Devic disease, is an autoimmune astrocytopathic disease characterized by transverse myelitis and optic neuritis. Most patients demonstrate a relapsing course with incomplete recovery between attacks, resulting in progressive disability. The pathogenesis involves production of aquaporin-4 antibodies (AQP4-IgG) by plasmablasts in peripheral circulation, disruption of the blood-brain barrier, complement-mediated astrocyte injury, and secondary demyelination. The diagnosis relies on characteristic clinical manifestations in the presence of serum AQP4-IgG positivity or specific neuroimaging findings, and exclusion of alternative etiologies. Current treatment involves aggressive immunosuppression with pulse-dose steroids during acute attacks and long-term immunosuppression for attack prevention.