IgG4 相关疾病 (IgG-RD) 是一组影响多种组织的纤维炎症性疾病，导致肿瘤样效应和/或器官功能障碍。单克隆丙种球蛋白病 (MGP) 是一组以浆细胞或淋巴细胞克隆增殖导致单克隆免疫球蛋白分泌为特征的疾病。过去几年已有 IgG4-RD 中 MGP 与浆细胞恶液质和淋巴肿瘤共存的病例报道。因此，IgG4-RD患者的M蛋白检查结果应谨慎解读。在此，我们报告一例 58 岁男性，有 2 型糖尿病病史，表现为颌下肿块、嗅觉丧失、淋巴结肿大、蛋白尿和肾功能损害。实验室测试显示高球蛋白血症以及 IgG4 (124 g/L) 和无血清轻链 (sFLC) 水平升高。血清蛋白电泳 (SPEP) 显示 M 峰值为 5.6 g/dL，免疫固定电泳 (IPE) 显示双克隆 IgG-κ 和 IgG-λ。该患者接受了骨髓、淋巴结和肾脏活检，排除了浆细胞疾病和淋巴瘤。他最终被诊断出患有 IgG4-RD 并伴有糖尿病肾病。该病例的研究结果强调，IgG4-RD 患者（尤其是多器官受累患者）中 B 细胞的显着激活可导致显着的高球蛋白血症以及高 sFLC 和 IgG4 水平，这在肾功能不全的情况下更为明显。相对高浓度的多克隆 IgG4 可以产生桥接 β 和 γ 部分的焦点带，这可能模仿 SPEP 上的单克隆带和 IFE 中的单克隆丙种球蛋白血症的外观。利妥昔单抗联合糖皮质激素治疗后，患者症状明显改善，且未检测到单克隆免疫球蛋白。© 2024。作者，获得国际风湿病协会联盟 (ILAR) 独家许可。

IgG4-related diseases (IgG-RDs) are a group of fibroinflammatory diseases that affect a variety of tissues, resulting in tumour-like effects and/or organ dysfunction. Monoclonal gammopathies (MGPs) are a group of disorders characterized by clonal proliferation of plasma cells or lymphoid cells resulting in the secretion of a monoclonal immunoglobulin. Cases of MGPs in IgG4-RDs coexisting with plasma cell dyscrasias and lymphoid neoplasms have been reported over the past few years. Therefore, the results of examinations of M protein in IgG4-RD patients should be interpreted with caution. Herein, we report the case of a 58-year-old male with a history of type 2 diabetes who presented with submandibular masses, anosmia, swollen lymph nodes, proteinuria, and renal impairment. Laboratory tests revealed hyperglobulinemia and elevated levels of IgG4 (124 g/L) and serum-free light chains (sFLCs). Serum protein electrophoresis (SPEP) revealed an M spike of 5.6 g/dL, and immunofixation electrophoresis (IPE) revealed biclonal IgG-κ and IgG-λ. The patient underwent bone marrow, lymph node, and kidney biopsy, which ruled out plasma cell disorders and lymphoma. He was finally diagnosed with an IgG4-RD comorbid with diabetic nephropathy. The findings in this case highlight that significant activation of B cells in IgG4-RD patients, especially those with multiorgan involvement can lead to significant hyperglobulinemia and high sFLC and IgG4 levels, which are more pronounced in the setting of renal impairment. Relatively high concentrations of polyclonal IgG4 can give rise to a focal band bridging the β and γ fractions, which may mimic the appearance of a monoclonal band on SPEP and monoclonal gammaglobulinemia in IFE. The patient experienced considerable improvement in his symptoms after rituximab combined with glucocorticoid therapy, and a monoclonal immunoglobulin was not detected.© 2024. The Author(s), under exclusive licence to International League of Associations for Rheumatology (ILAR).