病態には免疫応答が関与しており,アフェレシスによる治療効果が期待できる.PMとDMの共通の病理所見として,B細胞とCD4+T細胞が血管周囲や筋周膜に多く分布し,CD8+T細胞が筋内膜及び筋線維内に認める.PMでは,筋線維周囲にCD8+T細胞浸潤とMHC class Iの発現亢進がみられ,細胞傷害性T細胞が関与している.DMでは,筋線維束周辺の血管周囲のCD4+T細胞浸潤を認め免疫複合体などの液性因子による血管炎が関与している.
1) Choy EHS, Isenberg DA:Treatment of dermatomyositis and polymyositis. Rheumatology 2002;41:7-13 2) Arahata K, Engel AG:Monoclonal antibody analysis of mononuclear cells in myopathies. Quantitation of subsets according to diagnosis and sites of accumulation and demonstration and counts of muscle fibers invated by T cells. Ann Neurol 1986;16:193-208 3) 長谷麻子,荒畑喜一:多発筋炎・皮膚筋炎の免疫病理と治療.日内会誌1998;87:664-9 4) Kissel JT, Mendell JR, Rammohan KW:Microvascular deposition of complement membrane attack complex in dermatomyositis. N Engl J Med 1986;314:329-34 5) Dau PC:Plasmapheresis in idiopathic inflammatory myopathy. Experience with 35 patients. Arch Neurol 1981;38:544-52 6) Bennington JL, Dau PC:Patients with polymyositis and dermatomyositis who undergo plasmapheresis therapy. Pathologic findings. Arch Neurol 1981;38:553-60 7) Brewer EJ, Giannini EH, Rossen RD, et al:Plasma exchange therapy of a childhood onset dermatomyositis patient. Arthritis Rheum 1980;23:509-13 8) 吉岡美恵子,津田英夫,吉田弥太郎:Lymphoplasmapheresisによる難治性小児多発性筋炎の治療.臨床神経1984;24:214-7 9) Maruyama T, Koh CS, Inoue A, et al:Successful treatment of “steroid-immunosuppressant resistant” polymyositis with immunoadsorption. Rinsho Shinkeigaku 1991;31:1208-13 10) Miller FW, Leitman SF, Cronin ME, et al:Controlled trial of plasma exchange and leukapheresis in polymyositis and dermatomyositis. N Engl J Med 1992;326:1380-4