視神経脊髄炎関連疾患の病態生理と治療―update―

抄録

Neuromyelitis optica spectrum disorder (NMOSD) is diagnosed using international consensus criteria, a conceptual change from the original neuromyelitis optica (NMO) and considered beneficial for patients positive for the anti–aquaporin–4 (AQP4) antibody. When a diagnosis of NMOSD is confirmed, an established strategy for long–term immunosuppressive therapy will be chosen. Recent advances in understanding of the NMOSD pathomechanism have revealed that the anti–AQP4 antibody is likely the first to cause damage to astrocytes in the central nervous system (CNS) via complement activation, which then results in formation of a membrane attack complex. Another pathological process is an antibody–dependent cell–mediated cytotoxicity (ADCC) mechanism rendered by natural killer cells. Use of mild immunosuppression with corticosteroids and/or azathioprine has resulted in remarkable improvement in patient prognosis, with mycophenolate mofetil and tacrolimus also administered for this purpose. However, a substantial proportion of patients are refractory to those treatments, thus development of novel therapeutic options is mandatory. In this regard, repeated plasmapheresis for removal of pathological autoantibodies is an interesting candidate. Although anti–complement (C5) monoclonal antibody (MoAb) treatment is expensive, it is now available in Japan and has been shown to be a highly efficacious reagent that can largely prevent relapse. Furthermore, anti–IL–6 MoAb, which suppresses immune–mediated inflammation in the CNS, and anti–CD20 MoAb, which deletes B cells, i.e., a precursor of plasma cells, are promising treatment options. It should be noted that anti–AQP4 seronegative patients who are diagnosed in agreement with the NMOSD criteria have heterogenous etiologies. They may show an anti–myelin oligodendrocyte glycoprotein (MOG)–antibody syndrome that has good response to corticosteroids, while there is also a possibility that they are affected by opticospinal multiple sclerosis (MS), which should be controlled by disease–modifying drugs for MS. It is important to note that seronegative NMOSD patients require careful assessment of both neurological status and radiological findings irrespective of treatment selection.