Abstract：
Typically, myeloma cells express a monoclonal immunoglobulin (Ig), either heavy or light chain. Here, we present a case of multiple myeloma with clonal dual expression of kappa and lambda light chain in a 74-year-old woman. Awareness of rare biphenotypic myeloma is important for proper diagnostic workup. A 74-year-old woman underwent hip replacement with an incidental finding of 20% plasma cells in the femoral head. Subsequent bone marrow biopsy also showed about 30% of plasma cells negative for CD20, CD56, and CD117. Immunohistochemistry (IHC) and in situ hybridization studies showed a mixture of kappa and lambda plasma cells. Flow cytometry showed ambiguous results for cytoplasmic Ig light chains kappa and lambda. However, cyclin D1 was highly expressed by plasma cells, and increased free kappa light chains were identified in serum. Further investigation by double IHC demonstrated co-expression of kappa and lambda light chains in the same cells. Fluoresces in situ hybridization studies were positive for t(11;14)(q13;q32) and the deletion 13q. Since its first description by Taylor and Burns in 1974, the demonstration of restricted cytoplasmic Ig light chain expression by immunohistochemistry is 1 of the basic tools for corroborating clonality of the plasma cells in tissue biopsy. IHC results in myeloma with dual expression of Ig light chains may suggest polyclonal plasma cell population, especially when plasma cells do not form sheets in the bone marrow. In an appropriate clinical setting, other investigations are needed to exclude plasma cell neoplasm, even with seemingly \"polytypic\" results by IHC.
摘要：
通常,骨髓瘤细胞表达单克隆免疫球蛋白（Ig），重链或轻链。这里,我们介绍了一例多发性骨髓瘤，在一名74岁的女性中克隆性双重表达κ和λ轻链。了解罕见的双表型骨髓瘤对于正确的诊断检查很重要。一名74岁的妇女接受了髋关节置换术，偶然发现股骨头中有20％的浆细胞。随后的骨髓活检也显示约30%的浆细胞对CD20、CD56和CD117阴性。免疫组织化学（IHC）和原位杂交研究显示了κ和λ浆细胞的混合物。流式细胞术显示细胞质Ig轻链κ和λ的结果不明确。然而,细胞周期蛋白D1在浆细胞中高度表达，血清中游离κ轻链增加。通过双IHC的进一步研究证明了κ和λ轻链在相同细胞中的共表达。荧光原位杂交研究对t（11;14）（q13;q32）和缺失13q呈阳性。自1974年Taylor和Burns首次描述以来，通过免疫组织化学证明限制性细胞质Ig轻链表达是证实组织活检中浆细胞克隆性的基本工具之一。IHC结果在骨髓瘤中具有Ig轻链的双重表达可能提示多克隆浆细胞群，特别是当浆细胞在骨髓中不形成薄片时。在适当的临床环境中，需要进行其他检查以排除浆细胞肿瘤，即使IHC的结果看似“多型”。
