封入体筋炎の病態と原因

The Etiology and Pathogenesis of Sporadic Inclusion Body Myositis

封入体筋炎は，高齢者に好発する後天性筋疾患である。臨床的には，上肢遠位部と大腿四頭筋の筋萎縮・筋力低下が著明である。封入体筋炎は，多発筋炎や皮膚筋炎などの炎症性筋疾患の要素と，筋線維内への各種蛋白の沈着や空胞形成といった変性疾患の要素を併せ持つユニークな疾患であり，通常の免疫療法には治療抵抗性である。

Abstract

Sporadic inclusion body myositis (sIBM) is the most common acquired muscle disease in older individuals. Muscle weakness and atrophy in the quadriceps, wrist flexor, and finger flexors are the typical clinical findings in sIBM. The etiology and pathogenesis of sIBM are still poorly understood; however, genetic factors, aging, and environmental factors might possibly play a role. The pathological characteristics of sIBM include two unique features: inflammatory changes in muscle fibers, and cytoplasmic and intranuclear inclusions containing several Alzheimer-type proteins. Based on these pathological findings, there is a continuing debate on whether sIBM is primarily a T cell-mediated inflammatory myositis or a myodegenerative disorder characterized by abnormal protein aggregation, presence of inclusions bodies, and secondary inflammation. Unfortunately, sIBM is also generally refractory to immune therapy.