Although the clinical characteristics of this disease are similar to those of MS, recent clinical, histopathological, and serological findings strongly suggest the involvement of the humoral immune system in NMO [7–9] and that the detection of serum anti-aquaporin-4 (AQP4) antibody can be used to distinguish NMO from MS [10,11]. Here, AQP4 is linked to neuromyelitis optica.