Sporadic inclusion body myositis (sIBM) is a degenerative, intractable, inflammatory myopathy with an immune pathomechanism. We report on a case of a 44-year-old Japanese man who began developing progressive muscle weakness at age 40. Rheumatoid arthritis symptoms manifested at 43 with strongly positive anti-cyclic citrullinated peptide antibodies. Along with typical sIBM pathology, a muscle biopsy revealed dramatic inflammation with prominent perivascular B-cell infiltration forming ectopic lymphoid follicle-like structures (ELFLSs). Exome sequencing identified no causative variants of hereditary myopathy or immune disorders. A combination of immunotherapy slowed the progression of the muscular symptoms. This unusual form of sIBM, including earlier age at onset, a partial response to immunotherapy, and a histopathology presenting B-cell infiltrate with ectopic lymphoid follicle-like structures, indicates a possible association of rheumatoid arthritis and heterogeneity with the autoimmune involvement of sIBM. We review the clinical and pathological features of patients with rheumatoid arthritis associated sIBM in the literature.

散发性包涵体肌炎 (sIBM) 是一种具有免疫病理机制的退行性、顽固性、炎症性肌病。我们报告了一例 44 岁日本男性，他在 40 岁时开始出现进行性肌无力。类风湿性关节炎症状在 43 岁时出现，抗环瓜氨酸肽抗体呈强阳性。除了典型的 sIBM 病理学外，肌肉活检还显示有明显的炎症，伴有显着的血管周围 B 细胞浸润，形成异位淋巴滤泡样结构 (ELFLS)。外显子组测序未发现遗传性肌病或免疫疾病的致病变异。免疫疗法的组合减缓了肌肉症状的进展。这种不寻常的 sIBM 形式，包括发病年龄较早，对免疫疗法的部分反应，组织病理学显示 B 细胞浸润有异位淋巴滤泡样结构，表明类风湿性关节炎和异质性可能与 sIBM 的自身免疫参与有关。我们回顾了文献中与 sIBM 相关的类风湿性关节炎患者的临床和病理特征。