Membranous Nephropathy With Monoclonal IgM Lambda Deposits in a Patient With IgM Monoclonal Gammopathy: A Case Report

Clinical and Pathological Characteristics of Non-AL Amyloidosis MGRS: A Single-Center Experience Over 10 Years

Objective

Monoclonal gammopathy of renal significance (MGRS) is a heterogeneous and relatively recently defined disorder that encompasses many kidney and hematologic pathologies. MGRS remains a rare disease and there is a need for more literature regarding its treatment and outcomes. In this study, we share our center's experience with MGRS including incidence of different kidney pathologies, clone type, kidney and hematologic response, and progression-free survival.

Methods

Data from 35 patients diagnosed with MGRS excluding light-chain amyloidosis between 2013 and 2022 at a single Canadian tertiary care center were retrospectively analyzed. All cases required kidney biopsy. Initial treatment included regimens containing bortezomib, rituximab, or cyclosporine, or steroids only. Parameters studied included incidence of different kidney pathologies, clone type, depth of hematologic response, kidney survival (KS), overall survival (OS), and progression-free survival (PFS).

Results

Out of 35 patients, there were 10 cases of monoclonal immunoglobulin deposition disease, 8 of proliferative glomerulonephritis with immune deposits, 5 of microtubular immune deposits including immunotactoid and types 1 and 2 cryoglobulinemic nephropathy, 3 of C3 glomerulonephritis, and 9 of other diagnoses. There were 21 cases with a plasma cell clone identified in bone marrow, 2 each of B cell and low-grade lymphoma, 1 atypical T cell clone, and 9 cases without an expanded clone on bone marrow biopsy. A total of 6 patients required kidney replacement therapy and 4 patients died; the median PFS was 59.3 months. Very good partial hematologic response or better was significantly associated with decreased proteinuria but not preserved eGFR. There was a non-significant trend toward better PFS with hematologic response.

Conclusion

Our experience confirms that MGRS is a heterogeneous disease and adds to the literature concerning the diagnosis and treatment of MGRS. Successful treatment of the underlying hematologic disorder with targeted therapy is more likely to lead to an improvement in kidney function.

The fate of immune complexes in membranous nephropathy

The most characteristic feature of membranous nephropathy (MN) is the presence of subepithelial electron dense deposits and the consequential thickening of the glomerular basement membrane. There have been great advances in the understanding of the destiny of immune complexes in MN by the benefit of experimental models represented by Heymann nephritis. Subepithelial immune complexes are formed in situ by autoantibodies targeting native autoantigens or exogenous planted antigens such as the phospholipase A2 receptor (PLA2R) and cationic BSA respectively. The nascent immune complexes would not be pathogenic until they develop into immune deposits. Podocytes are the major source of autoantigens in idiopathic membranous nephropathy. They also participate in the modulation and removal of the immune complexes to a large extent. The balance between deposition and clearance is regulated by a wide range of factors such as the composition and physicochemical properties of the immune complexes and the complement system. Complement components such as C3 and C1q have been reported to be precipitated with the deposits whereas a complement regulatory protein CR1 expressed by podocytes is involved in the phagocytosis of immune complexes by podocytes. Podocytes regulate the dynamic change of immune complexes which is disturbed in membranous nephropathy. To elucidate the precise fate of the immune complexes is essential for developing more rational and novel therapies for membranous nephropathy.

The Prevalence, Characteristics, and Putative Mechanisms of Dual Antigen-Positive Membranous Nephropathy: The Underestimated Condition

Following the discovery of podocyte phospholipase A2 receptor and thrombospondin type-1 domain-containing 7A, various potential target antigens for membranous nephropathy (MN) have been reported one after another. MN target antigens have now been identified in a significant proportion of patients, and a new classification framework classifies patients with MN based on the detected antigen and associated disease phenotype. A serology-based approach that does not require a histological diagnosis for patients suspected of having MN has also been proposed. However, there have been cases in which dual positivity for MN antigens and/or corresponding antibodies has been shown. Importantly, some of them showed a transition of the affected patient's immune responses to MN antigens, suggesting that serological diagnosis changes depending on the timing of the analysis. In this review, we provide detailed information on these cases and present an overview of our recent understanding of their putative mechanisms involved in these cases. Greater awareness is required to adequately recognize and develop appropriate therapeutic strategies for this condition.

Concurrent Crystalline Light-Chain Proximal Tubulopathy and Membranous Nephropathy: A Case Report and Literature Review

Light-chain proximal tubulopathy (LCPT) is typically characterized by the intracytoplasmic deposition of light chains within the proximal tubular epithelial cells, which is usually classified into crystalline and noncrystalline subgroups. Membranous nephropathy (MN) is a common glomerular disease characterized by diffused subepithelial electron-dense deposits along the capillary loop accompanied by the effacement and microvillus transformation of the foot process. Here, we report a biopsy-confirmed case of a concurrence of LCPT with crystals (κ light chains restricted) and antigen-undetermined MN in a male patient. The patient presented with low-molecular-weight proteinuria, increased serum creatinine levels, and incomplete Fanconi syndrome. To our knowledge, this is the first report of a concurrence of LCPT and independent MN of unknown target antigens, which may enrich our recognition of monoclonal gammopathy of renal significance with synchronous MN.

Discordance of light chain isotypes between serum and glomerular deposits in proliferative glomerulonephritis with monoclonal IgG deposits: a case report and review of the literature

BACKGROUND

Proliferative glomerulonephritis with monoclonal immunoglobulin G (IgG) deposits (PGNMID) is a disease entity with nonorganized granular glomerular deposition with monoclonal proteins of both heavy and light chains. Dysproteinemia was observed in only 30% of the patients with PGNMID. We herein report a case of PGNMID with discrepancy between serum and glomerular deposits.

CASE PRESENTATION

The patient was a 50-year-old man who had been followed at a local clinic due to hypertension, type 2 diabetes, hyperlipidemia, hyperuricemia, fatty liver, and obesity. Proteinuria had been noted five years previously, and he had been referred to a hematology department due to hyperproteinemia, high gamma globulin, and κ Bence-Jones protein (BJP) positivity one year previously. Bone marrow aspiration showed 5% plasma cells, and he was referred to the nephrology department to evaluate persistent proteinuria. He was hypertensive, and his estimated glomerular filtration rate was 54.2 ml/min/1.73 m2. His urinary protein level was 0.84 g/g⋅Cr. Urine and serum immunofixation showed BJP-κ type and IgG-κ type, respectively. Kidney biopsy showed an increase in mesangial cells and matrix without nodular lesions under a light microscope. Immunofluorescence microscopy showed granular deposits of IgG and C3 on the capillary wall and weak positivity for C1q. IgG3 was predominant among the IgG subclasses, and intraglomerular κ and λ staining was negative for κ and positive for λ. Direct fast scarlet staining was negative. Electron microscopy showed lumpy deposits without a fibrillar structure in the subepithelial area. Based on the above findings, a diagnosis of membranous nephropathy-type PGNMID was made. Since proteinuria increased gradually after three years of treatment with valsartan (40 mg, daily), oral prednisolone (30 mg, daily) was initiated, which led to decreased proteinuria. The dose of oral prednisolone was gradually tapered to 10 mg per day. At that time, proteinuria was 0.88 g/g⋅Cr. We found 204 cases in 81 articles in the PubMed database, among which 8 showed discrepancy in the heavy and/or light chains between serum and kidney.

CONCLUSIONS

We experienced a case of membranous nephropathy-type PGNMID with discrepancy in light chains between serum and kidney that was successfully treated with oral prednisolone.

Chronic Graft-versus-host Disease-associated Membranous Nephropathy Following Bone Marrow Transplantation, Successfully Treated with Rituximab

A 67-year-old woman who had undergone bone marrow transplantation 2 years previously for acute myeloid leukemia (AML) developed complications of chronic graft-versus-host disease (cGVHD). She thereafter also developed nephrotic syndrome, and membranous nephropathy (MN) was diagnosed by a renal biopsy. Although the causative antigens of the MN were not detected, immunofluorescence staining showed codominant deposition of immunoglobulins G2 and G3, a finding indicating secondary MN, thereby suggesting an association between MN and cGVHD. Rituximab treatment was initiated, and her nephrotic syndrome gradually improved without relapse of AML. Our present case suggests that rituximab is a safe and effective therapeutic option for cGVHD-associated MN.