The diagnostic value of kappa/lambda ratios determined by immunohistochemistry in the differentiation of plasma cell myeloma from reactive plasmacytosis

Context: Plasma cell myeloma (PCM) is the second-most common B-cell malignancy in western countries. In this disease, the bone marrow is infiltrated by monoclonal plasma cells, which may secrete immunoglobulin light chains. In this line, reactive plasma cells may infiltrate into the bone marrow that can lead to misdiagnosis of the disease. Aims: The purpose of this study was to determine monoclonality using immunohistochemistry (IHC) for kappa and lambda light chains in bone marrow biopsy (BMB) specimens. These findings may be useful in the differentiation of PCM from reactive plasmacytosis. Materials and Methods: In this study, BMB paraffin blocks from 90 patients including 45 cases of PCM and 45 patients with reactive plasmacytosis were collected at the pathology center of Imam Reza Hospital from 2006 to 2014. IHC staining for CD138 and Kappa-Lambda light chains were performed. Relative frequencies of Kappa to Lambda light chain positive cells were calculated. Statistical Analysis Used: The results were analyzed with spss16 and Rx64 3.1.2 software. Results: Strong Kappa staining was found in 37 of 45 PCM cases (82.2%), with the ratio of Kappa/Lambda>3 and eight other cases (17.8%) expressed Kappa/Lambda<0.48. In cases with reactive plasmacytosis, K/L ratio was 0.48≤ × ≤3. Sensitivity and specificity for the diagnosis of PCM versus reactive plasmacytosis were 100% and 97.8%, respectively. Conclusions: Results indicated that immunohistochemical staining of CD138, kappa, and lambda light chains could be considered as an assured and reliable assay for the diagnosis of monoclonal plasma cells and differentiating it from other hematological malignancies.