In the group of subjects with optic-spinal MS (OSMS), the main lesions are typically confined to the optic nerve and spinal cord. In Asians, OSMS has similar features to the relapsing remitting form of neuromyelitis optica (NMO) seen in Westerners. It is still a matter of debate whether NMO represents a disease entity in itself or whether it is a subform of MS. Early differentiation of NMO from MS is highly desirable, as treatment options and prognoses differ widely. Recently, a new serum autoantibody (NMO-IgG) has been detected in NMO subjects. The binding sites of this autoantibody were reported to colocalize with aquaporin 4 (AQP4) water channels. Optic-spinal MS is sometime suggested to be NMO based on the frequent detection of the anti-AQP4 IgG antibody. In Taiwan, study has shown that 56% of MS subjects were of the optic-spinal type.