Light Chain Restriction in Proximal Tubules-Implications for Light Chain Proximal Tubulopathy

Monoclonal gammopathy (MG) causes various nephropathies, which may suffice for cytoreductive therapy even in the absence of diagnostic criteria for multiple myeloma or B-cell non-Hodgkin lymphoma. The aim of this study was to better understand the significance of light chain (LC) restriction or crystals (LC-R/C) in proximal tubules in the spectrum of LC-induced nephropathies. A consecutive cohort of 320 renal specimens with a history of B-cell dyscrasia was characterized. Special attention was paid to immunohistochemical LC restriction in proximal tubules, tubular crystals or constipation, and ultrastructural findings. Complementary cell culture experiments were performed to assess the role of LC concentrations in generating LC restriction. Light chain restriction or crystals in proximal tubules was found in a quarter of analyzed cases (81/316) and was associated with another LC-induced disease in 70.4% (57/81), especially LC cast-nephropathy (cast-NP) and interstitial myeloma infiltration. LC restriction without significant signs of acute tubular injury was observed in 11.1% (9/81). LC-R/C was not associated with inferior renal function compared to the remainder of cases, when cases with accompanying cast-NP were excluded. Besides crystals, cloudy lysosomes were significantly associated with LC-R/C on an ultrastructural level. In summary, LC-R/C is frequent and strongly associated with cast-NP, possibly indicating that a high load of clonal LC is responsible for this phenomenon, supported by the observation that LC restriction can artificially be generated in cell culture. This and the lack of significant tubular injury in a subgroup imply that in part LC-R/C is a tubular trafficking phenomenon rather than an independent disease process.

The cut-offs for kappa/lambda ratio in bone marrow immunohistochemistry for the diagnosis of multiple myeloma

Objective: The previously reported kappa/lambda ratio cut-offs for plasma cell clonality by immunohistochemistry were in different values. This study aimed to identify the cut-offs with the highest accuracy for the diagnosis of multiple myeloma. Methods: Bone marrow specimens consecutively recruited between January 2011 and March 2019. The patients were at least 18 years old with clinical suspicion of multiple myeloma and had bone marrow plasma cell ≥10% by CD138 immunohistochemistry. The index test was immunohistochemical stains for plasma cell kappa/lambda ratio. The reference standard to classify as multiple myeloma required meeting any of the following (1) kappa/lambda ratio ≤1/16 or ≥16, (2) abnormal plasma cell morphology, and (3) monoclonal immunoglobulin. Results: From 147 specimens (70 multiple myelomas and 77 reactive plasmacytosis), our cut-offs kappa/lambda ratio for light chain restriction at ≤1/7 or ≥9 yielded an area under the receiver operating characteristic curve of 1.0000 while ≤1/16 or ≥16 yielded 0.9643 (p-value 0.0212). Conclusion: The cut-offs for kappa/lambda ratio at ≤1/7 or ≥9 for diagnosis of multiple myeloma yielded the highest diagnostic accuracy. The suggested cut-offs could be of potential value in resource-limited laboratories.

Cutaneous follicle center lymphomas with plasmacytic differentiation

Follicle center lymphomas, including primary cutaneous follicle center lymphoma (PCFCL), may rarely show plasmacytic differentiation. Such cases can pose a diagnostic challenge and can be mistaken for other lymphomas that more commonly include plasma cells. Here, we report four cases of PCFCL and one case of systemic follicular lymphoma involving the skin with associated monotypic plasma cells, including the clinical, morphologic and immunophenotypic features.

An Endoscopic Biopsy Specimen Contains Adequate Lymphocytes for Flow Cytometric Analysis of Light Chain Expression in the Gastrointestinal Mucosa

OBJECTIVE

Flow cytometry has not been widely used in routine clinical practice for the diagnosis of gastrointestinal lymphoma; this is mainly because of the absence of an appropriate protocol. Here, we established a protocol for flow cytometric analysis of a single biopsy specimen from the gastrointestinal mucosa and investigated its sensitivity and specificity.

DESIGN

In this prospective study, we enrolled patients with previously diagnosed gastrointestinal lymphoma and patients with gastrointestinal lesions that were suspected to be lymphoma.

RESULTS

Overall, 15 patients with gastric extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (N=8), duodenal follicular lymphoma (grade 1; N=5), and benign lymphoid hyperplasia (ileum, N=1, and rectum, N=1) were included in this study. Of these, lymphocytes were isolated from 14 patients (93.3%). There were 200,000-1,500,000 viable cells per patient. Biopsy specimens from 10 out of the 12 patients with lymphoma were positive for light chain restriction; the two patients with benign lymphoid hyperplasia showed negative results.

CONCLUSIONS

An adequate number of lymphocytes for flow cytometry could be isolated from a single specimen of endoscopic mucosal biopsy from 93.3% of the patients. Overall, the sensitivity of flow cytometric analysis of light chain expression for the diagnosis of B-cell lymphoma was 83.3%, and the specificity was 100%. Although further investigation is required as the sample size of the present study was small, our study suggests a potential option for diagnosing B-cell lymphoma in the gastrointestinal mucosa.

Localized accumulation of kappa restricted Russell body-containing plasma cells in tonsil

An abnormal clonal plasma cell proliferation with Russell bodies is rare in chronic inflammatory reactions in adult patients. We describe the first case of light chain restricted Russell body accumulation within germinal centers of lymphoid follicles of the tonsil in a child. This should not be confused with a neoplastic process.

Ultrasensitive automated RNA in situ hybridization for kappa and lambda light chain mRNA detects B-cell clonality in tissue biopsies with performance comparable or superior to flow cytometry

The assessment of B-cell clonality is a critical component of the evaluation of suspected lymphoproliferative disorders, but analysis from formalin-fixed, paraffin-embedded tissues can be challenging if fresh tissue is not available for flow cytometry. Immunohistochemical and conventional bright field in situ hybridization stains for kappa and lambda are effective for evaluation of plasma cells but are often insufficiently sensitive to detect the much lower abundance of light chains present in B-cells. We describe an ultrasensitive RNA in situ hybridization assay that has been adapted for use on an automated immunohistochemistry platform and compare results with flow cytometry in 203 consecutive tissues and 104 consecutive bone marrows. Overall, in 203 tissue biopsies, RNA in situ hybridization identified light chain-restricted B-cells in 85 (42%) vs 58 (29%) by flow cytometry. Within 83 B-cell non-Hodgkin lymphomas, RNA in situ hybridization identified restricted B-cells in 74 (89%) vs 56 (67%) by flow cytometry. B-cell clonality could be evaluated in only 23/104 (22%) bone marrow cases owing to poor RNA preservation, but evaluable cases showed 91% concordance with flow cytometry. RNA in situ hybridization allowed for recognition of biclonal/composite lymphomas not identified by flow cytometry and highlighted unexpected findings, such as coexpression of kappa and lambda RNA in 2 cases and the presence of lambda light chain RNA in a T lymphoblastic lymphoma. Automated RNA in situ hybridization showed excellent interobserver reproducibility for manual evaluation (average K=0.92), and an automated image analysis system showed high concordance (97%) with manual evaluation. Automated RNA in situ hybridization staining, which can be adopted on commonly utilized immunohistochemistry instruments, allows for the interpretation of clonality in the context of the morphological features in formalin-fixed, paraffin-embedded tissues with a clinical sensitivity similar or superior to flow cytometry.

Type I Cryoglobulinemic Nephritis in a Patient of Monoclonal Gammopathy of Renal Significance

Monoclonal gammopathy of renal significance is a recently described entity in which a small B-cell clone not meeting the criteria for the diagnosis of multiple myeloma produces renal disease usually through deposition of a secreted monoclonal immunoglobulin. Here, we describe a case of Type I cryoglobulinemic glomerulonephritis diagnosed on a kidney biopsy and caused by a monoclonal IgM produced by a small bone marrow clone. The patient made a complete renal recovery after chemotherapy to suppress the clone.