Neuromyelitis optica (NMO) spectrum disorders (NMOSDs) are inflammatory disorders of the central nervous system (CNS) characterized by attacks of optic neuritis or myelitis or both. The NMOSDs are the first inflammatory demyelinating diseases of the CNS for which a specific tissue target molecule has been identified: the astrocytic water channel aquaporin 4. They include NMO and limited NMO forms (predominantly occurring in patients who are seropositive for aquaporin 4–IgG and have had ≥1 attack of optic neuritis or myelitis only). The NMOSDs are now considered IgG-mediated autoimmune astrocytopathic diseases. The prognosis of untreated NMO is significantly worse than that of multiple sclerosis because recovery from attacks is usually incomplete, and incremental attack-related disability is more likely to develop. Early initiation of immunotherapy with successful prevention of attacks will probably have a greater effect on the natural history of NMO than on multiple sclerosis. The immunosuppressants most commonly prescribed for maintenance of remission, azathioprine or mycophenolate mofetil (with or without prednisone) and rituximab, have been assessed in small, uncontrolled studies only.
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