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.