NMOの抗AQP4抗体からみた治療法の選択

Treatment and Clinical Management of Patients with Neuromyelitis Optica and Anti-aquaporin 4 Antibody

はじめに

　多発性硬化症（multiple sclerosis：MS）は再発と寛解を繰り返し，時間的・空間的多発性を特徴とする中枢神経系の非化膿性炎症性脱髄疾患である。わが国では再発寛解型MSと診断される症例を，さらに病変分布によって分類してきた。つまり，大脳や小脳，脳幹など中枢神経系全般にわたり多巣性の病巣を生じるものを通常型MS（conventional MS：CMS）と呼び，視神経と脊髄が選択的かつ高度に障害される症例を視神経脊髄型MS（optic-spinal MS：OSMS）と呼んで両者を区別してきた。後者はわが国のMSに特徴的な病型とされてきたが，NMO-IgG（anti-aquaporin 4 antibody：抗AQP4抗体）の発見により，その典型例は欧米におけるneuromyelitis optica（NMO）と同一疾患・病態であることが明らかとなった。MSとNMOを鑑別することは治療法選択の観点から特に重要で，両者の早期鑑別には抗AQP4抗体の有無を検索することが有用である。本稿では，NMOの早期診断と早期治療，適切な再発予防対策の重要性について考察したい。

Abstract

　Neuromyelitis optica (NMO) is a unique inflammatory condition characterized by selective involvement of the optic nerves and spinal cord.　The cardinal features of NMO and a tendency of recurrence led to the classification of NMO as a subtype of multiple sclerosis (MS); however,it can be distinguished from MS on the basis of clinicoradiological and serological findings. In paticular,NMO is characterized by the presence of spinal cord lesions that are longer than the total length of 3 vertebral segments and presence of anti-aquaporin 4 antibodies.　Secondary progression of this condition is usually not observed,and therapy for NMO patients is designed to prevent acute exacerbations and limit irreversible neurological disability.　Intravenous administration of a high dose of methylprednisolone is a standard treatment for patients with acute exacerbations of this condition,and patients with refractory cases are often responsive to plasmapheresis.　To reduce the frequency of relapses and severity,standard therapies for MS,such as interferon-beta therapy,are not effective; further,a long-term immunosuppressive therapy is required for NMO patients.　Immunosuppressive therapies often involve oral administration of prednisolone with or without azathioprine; patients who are refractory to the oral therapy may be treated by parental administration of cyclophosphamide,mitoxantrone,or rituximab.　At present,there is no cure for NMO; early and precise diagnosis is critical to initiate immunosuppressive therapy for prevention of relapse.