Rheumatoid arthritis (RA) is a chronic autoimmune disease affecting primarily joints and an increased risk of developing malignant lymphomas in RA has been well reported. However, primary lymphoma in a joint in RA patient is rare. We report the case of a 65-year-old man with RA suffering from pain and swelling of left sternoclavicular (SC) joint, which was not relieved by adding low-dose glucocorticoid. Magnetic resonance imaging (MRI) showed a para-osseous soft tissue swelling around the SC joint and a fracture of proximal clavicle. Histology of the soft tissue demonstrated diffuse large B-cell lymphoma and the patient subsequently underwent R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone) chemotherapy. He was successfully treated with six cycles of R-CHOP chemotherapy, with discontinuation of MTX, resulting in a complete response. We performed a literature review and identified nine cases of lymphoma which involved joints in patients with rheumatoid arthritis. This is the first described case of a primary large B-cell lymphoma involving the unilateral SC joint in a patient with RA, which was initially confused with aggravation of RA. Therefore, malignant lymphoma should be considered in the differential diagnosis when a RA patient develops monoarthritis with spontaneous fracture, even without B symptoms.

中文翻译：

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弥漫性大B细胞淋巴瘤累及左侧锁骨关节，模仿类风湿关节炎发作：病例分析。

类风湿关节炎（RA）是一种慢性自身免疫性疾病，主要影响关节，RA中发生恶性淋巴瘤的风险增加已有报道。但是，RA患者的关节中原发性淋巴瘤很少见。我们报道了一例65岁的RA患者，患有左胸锁骨（SC）关节疼痛和肿胀，但不能通过添加小剂量糖皮质激素来缓解。磁共振成像（MRI）显示SC关节周围的骨旁软组织肿胀和锁骨近端骨折。软组织的组织学表现为弥漫性大B细胞淋巴瘤，患者随后接受了R-CHOP（利妥昔单抗，环磷酰胺，阿霉素，长春新碱和泼尼松龙）化疗。他已通过六个周期的R-CHOP化疗成功治疗，并停用了MTX，导致了完整的回应。我们进行了文献综述，并确定了9例风湿性关节炎患者的淋巴瘤涉及关节。这是首次描述的原发性大B细胞淋巴瘤，累及RA患者，单侧SC关节，最初与RA加重相混淆。因此，当RA患者发展为自发性骨折甚至无B症状的单关节炎时，在鉴别诊断中应考虑恶性淋巴瘤。