Background: Neuromyelitis optica (NMO) is a neurological disease characterized by optic neuritis and transverse myelitis with long spinal cord lesion. Recently, NMO-IgG, which recognizes the aquaporin-4 (AQP-4), was identified in sera from patients with NMO. AQP-4 is a water channel expressed in astrocytes and ependymal cells throughout the brain and spinal cord