Neuromyelitis optica

Neuromyelitis optica (NMO, Devic's disease) is a neurologic disease characterized by severe optic neuritis and transverse myelitis. In Japan, NMO has been classified as a type of multiple sclerosis (MS) with a unique lesion distribution (optic-spinal MS). However, unlike the classical features seen with MS, NMO is different in that blindness and bilateral visual disturbance due to optic chiasmal lesions are not rare, spinal cord lesions are often longer than 3 vertebral segmerits, and the oligoclonal IgG bands are mostly negative. Recently, aquaporin-4 (AQP4) antibody, a serum NMO-specific autoantibody, has been discovered. Pathological studies revealed in NMO patients there was the loss of AQP4 along with glial fibrillary acidic protein (GFAP). This strongly suggests that there is astrocytic damage, which is unique to NMO. Moreover, corticosteroid and immunosuppressants reduce the relapse rate in NMO while immunomodulating drugs, which include interferon-beta, are the first-line therapy in MS. When taken together, it is clear that NMO is a clinical entity that is distinct from MS, and thus, classifying NMO as optic-spinal MS can no longer be considered to be appropriate.