The clinicopathologic characteristics of kidney diseases related to monotypic IgA deposits

A case of heavy-chain deposition disease with good long-term renal survival and a literature review

BACKGROUND

Monoclonal immunoglobulin deposition disease (MIDD) is characterized by the deposition of nonamyloid monoclonal immunoglobulin and its free fragment light chain and/or heavy chain in systemic tissues and organs, and the kidney is most vulnerable organs. MIDD can be divided into three types: light-chain deposition disease (LCDD), light and heavy chain deposition disease (LHCDD), and heavy-chain deposition disease (HCDD), of which LHCDD and HCDD are rarer (Bridoux et al. in Kidney Int 2015;87:698-711; Preud'homme et al. in Kidney Int 1994;46:965-72). Poor outcome in most HCDD, but in this paper, we will report a case of HCDD with good long-term renal survival and review the literature for reference.

CASE PRESENTATION

A 32-year-old man presented to our department with skin laxity and nephritic syndrome, accompanied by an significant increase of serum creatinine and received short-term hemodialysis treatment. Both the blood and urine free light chain ratio increased significantly. Renal biopsy showed mesangial nodular glomerulosclerosis on light microscopy, and immunofluorescence staining showed positivity for γ-heavy chain (HC), with negative light chain (LC) staining; the diagnosis was considered HCDD. After six courses of bortezomib combined with dexamethasone chemotherapy and thalidomide 100 mg/day, the renal function gradually recovered, while also with proteinuria and hematuria significantly improved. The blood and urine free light chain ratio decreased to normal. Until now, the patient has been followed for four years, and long-term renal survival has been observed.

CONCLUSION

Herein, we report a case presenting with proteinuria, hematuria, renal impairment, and skin laxity, and a renal biopsy showed linear IgG deposition in the glomerular basement membranes and tubular basement membrane. However, they ultimately proved to have HCDD. Bortezomib combined with dexamethasone, and oral thalidomide led to a good long-term renal survival. We also provide a review of currently available literature, and this is the first large-scale review summarizing the characteristics of HCDD up to date.

Diagnostic Challenges and Emerging Pathogeneses of Selected Glomerulopathies

Recent progress in glomerular immune complex and complement-mediated diseases have refined diagnostic categories and informed mechanistic understanding of disease development in pediatric patients. Herein, we discuss selected advances in 3 categories. First, membranous nephropathy antigens are increasingly utilized to characterize disease in pediatric patients and include phospholipase A2 receptor (PLA2R), Semaphorin 3B (Sema3B), neural epidermal growth factor-like 1 (NELL1), and protocadherin FAT1, as well as the lupus membranous-associated antigens exostosin 1/2 (EXT1/2), neural cell adhesion molecule 1 (NCAM1), and transforming growth factor beta receptor 3 (TGFBR3). Second, we examine advances in techniques for paraffin and light chain immunofluorescence (IF), including the former's function as a salvage technique and their necessity for diagnosis in adolescent cases of membranous-like glomerulopathy with masked IgG kappa deposits (MGMID) and proliferative glomerulonephritis with monotypic Ig deposits (PGNMID), respectively. Finally, progress in understanding the roles of complement in pediatric glomerular disease is reviewed, with specific attention to overlapping clinical, histologic, and genetic or functional alternative complement pathway (AP) abnormalities among C3 glomerulopathy (C3G), infection-related and post-infectious GN, "atypical" post-infectious GN, immune complex mediated membranoproliferative glomerulonephritis (IC-MPGN), and atypical hemolytic uremic syndrome (aHUS).

Immunofluorescence Use and Techniques in Glomerular Diseases: A Review

Background

Immunofluorescence (IF) studies play an essential role in the evaluation of medical renal biopsies. Particularly, in the study of renal glomerular diseases, where it provides fundamental data for the diagnosis, classification, and etiology of the glomerular pathologies. Diverse techniques may be used to optimize the utilization of IF studies, from variations on the test methodologies to expertise on the interpretation of the results and knowledge of potential pitfalls.

Summary

This manuscript presents a brief review on the history of IF and its utilization in kidney pathology, followed by a description of the IF methods, including the use of IF on paraffin-embedded tissue (paraffin IF), and other novel techniques. Guidelines on how to best report IF findings are reviewed, along with a description of antibodies commonly used in glomerular diseases, highlighting their distribution within the normal kidney and potential pitfalls in interpretation. Finally, the use and interpretation of IF are discussed in more detail in individual entities on a range of glomerular diseases.

Key Messages

IF is crucial for interpretation of renal biopsies and diagnosis of glomerular diseases. Knowledge of IF techniques, alternative procedures, its use and proper interpretation is essential for optimal utilization of IF in renal pathology, and this review proposes to serve as a simplified and practical guide on this topic.

IgA nephropathy to proliferative glomerulonephritis with monoclonal IgAκ deposits: a pattern switch

We report the case of a 31-year-old male who presented with repeated episodes of nephritic-nephrotic syndrome in concomitance with infection. IgA was diagnosed and was initially responsive to treatment with immunosuppressors but further disease flare did not respond to treatment. Based on three consecutive renal biopsies over 8 years, a pattern switch from endocapillary proliferative IgA nephropathy to membranous proliferative glomerulonephritis with monoclonal IgAκ deposits was observed. Bortezomib-dexamethasone combination therapy finally led to a favorable renal response. This case provides new insights into the pathophysiological mechanisms of proliferative glomerulonephritis with monoclonal immunoglobin deposits (PGNMID), highlighting the importance of repeat renal biopsies and routine evaluation of monoclonal immunoglobin deposits in proliferative glomerulonephritis with refractory nephrotic syndrome.

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.

Monoclonal gammopathy of renal significance: Multidisciplinary approach to diagnosis and treatment

Monoclonal gammopathy of renal significance (MGRS) is a hemato-nephrological term referring to a heterogeneous group of kidney disorders characterized by direct or indirect kidney injury caused by a monoclonal immunoglobulin (MIg) produced by a B cell or plasma cell clone that does not meet current hematologic criteria for therapy. MGRS-associated kidney diseases are diverse and can result in the development of end stage kidney disease (ESKD). The diagnosis is typically made by nephrologists through a kidney biopsy. Many distinct pathologies have been identified and they are classified based on the site or composition of the deposited Mig, or according to histological and ultrastructural findings. Therapy is directed towards the identified underlying clonal population and treatment decisions should be coordinated between hematologists and nephrologists in a multidisciplinary fashion, depend on the type of MGRS, the degree of kidney function impairment and the risk of progression to ESKD.

The significance of galactose-deficient immunoglobulin A1 staining in kidney diseases with IgA deposition

BACKGROUND

This study investigated the significance of galactose-deficient immunoglobulin A1 staining in kidney diseases with IgA deposition.

METHODS

A total of 120 patients with IgA-dominant deposition in kidney tissues were enrolled and divided into four groups: primary IgA nephropathy (PIgAN), secondary IgA nephropathy (SIgAN), monotypic IgA nephropathy (MIgAN), and IgA variant monoclonal gammopathy of renal significance (IgA-MGRS). KM55 (the antibody of galactose-deficient immunoglobulin A1), IgA subtypes, and complement pathway factors (properdin, C4d, and C1q) were detected through immunofluorescence or immunohistochemistry analysis.

RESULTS

KM55 and IgA double staining showed colocalization within glomeruli in all cases except for IgA-MGRS, which showed negative or weak staining of KM55 but strong staining of IgA. The PIgAN group showed the highest intensity of KM55 and KM55/IgA ratio, while these values in the IgA-MGRS group were the lowest (P < 0.01). A KM55/IgA quantified ratio of 0.78 was the optimal cut-off value to distinguish PIgAN from SIgAN, whereas a cut-off value of 0.21 was optimal to distinguish between MIgAN and IgA-MGRS. The clinicopathological characteristics showed significant differences as the groups were divided by diseases with optimal cut-off values, and these differences corresponded to the pathogenesis of each disease entity.

CONCLUSIONS

PIgAN, SIgAN, and MIgAN are caused by the deposition of abnormally glycosylated IgA1 whereas IgA-MGRS is not. The KM55/IgA quantified ratio is valuable in distinguishing PIgAN from SIgAN, as well as MIgAN from IgA-MGRS.

Proliferative glomerulonephritis with monoclonal immunoglobulin G3 lambda deposits accompanied by glomerular positive staining for nephritis-associated plasmin receptor and related plasmin activity: A report of two cases

Proliferative glomerulonephritis with monoclonal immunoglobulin (Ig) G deposits (PGNMID) is a relatively uncommon entity of monoclonal gammopathy of renal significance, and its detailed pathogenesis is not well understood. We, herein, report two cases of patients with PGNMID; their renal biopsy showed glomerular histological features of membranoproliferative glomerulonephritis pattern with endocapillary proliferation accompanied by non-organized granular electron-dense deposits that consisted of monoclonal IgG3-lambda. Neither symptomatic episodes of preceding infection nor infection foci were found in both patients; however, glomerular positive staining for nephritis-associated plasmin receptor (NAPlr) and related plasmin activity were observed. Although NAPlr was originally considered as a candidate nephritogenic protein for post-streptococcal acute glomerulonephritis, its positive staining and related plasmin activity have been observed in glomeruli of various cases with bacterial infection-related glomerulonephritis and is considered to be a general histological biomarker of infection-related glomerulonephritis. The present cases suggest that evaluation of immunoreactivity for NAPlr and related plasmin activity in glomeruli provides an important clue regarding the infection-related pathogenesis of PGNMID.

An Unusual Case of Seronegative Cryoglobulinemic Glomerulonephritis with Dominant Organized IgA Deposits Associated with Staphylococcal Infection: Casual or Causal Relationship?

Introduction

Cryoglobulinemia refers to the presence of cryoglobulins (CGs) in the serum, encompassing a group of diseases caused by the type of circulating GC. Cryoglobulinemic glomerulonephritis (CryoGN) is the principal manifestation of renal involvement. The diagnosis may be challenging because the hallmark of cryoglobulinemia is the detection of CG in the serum. However, cases of CryoGN without serological evidence of CGs are not uncommon in clinical practice, often diagnosed by anatomopathological findings in the renal biopsy.

Case Presentation

We report the case of an 86-year-old male who developed renal impairment, nephritic syndrome, and nephrotic-range proteinuria, without serological evidence of CGs, associated with staphylococcal bacteremia without apparent focus. Renal biopsy and pathological examination showed a membranoproliferative glomerulonephritis pattern with CD61-negative pseudothrombi. Immunofluorescence microscopy showed atypical IgA-dominant deposits. Electron microscopy revealed amorphous subendothelial and mesangial deposits and organized electrodense deposits within capillary loops (pseudothrombi) with microtubular substructure measuring 20-40 nm in thickness. These findings were consistent with seronegative CryoGN and microtubular organized atypical IgA-dominant deposits.

Discussion

In this report, we discuss the clinical, analytical, and histopathological findings of a rare case of CryoGN without serological evidence of CGs. Regarding the etiology that triggered the glomerular disease in our patient, we conducted an exhaustive study in order to determine the underlying cause of CryoGN. At the time of biopsy, the patient had an active staphylococcal bacteremia. There are reports that postulate that staphylococcal antigens drive activation of immune system and in consequence, could cause this rare form of IgA-dominant glomerulonephritis with cryoglobulinemic features. After ruling out other causes of cryoglobulinemia, we discuss a plausible causal relationship of the staphylococcal infection in the pathogenesis of CryoGN in our patient.

Kidney Transplantation in Patients With Monoclonal Gammopathy of Renal Significance

Monoclonal gammopathy of renal significance (MGRS) defines disorders characterized by direct or indirect kidney injury caused by a monoclonal immunoglobulin produced by a B-cell or plasma-cell clone that does not meet current hematologic criteria for therapy. MGRS-associated kidney diseases are diverse and can result in the development of end-stage kidney disease. The current paradigm states that the underlying hematologic condition should be treated and in deep remission before kidney transplantation can be performed because recurrence has been reported for all MGRS-associated kidney diseases. However, we suggest that decisions regarding kidney transplantation in MGRS patients should be individualized considering many factors such as the subtype of MGRS-associated kidney disease, patient age and comorbidity, presence and risk of extrarenal complications, estimated waiting time, the availability of a living kidney donor, and previous hematological treatment and response. Thus, kidney transplantation should be considered even in treatment-naive patients, with hematological treatment initiated after successful kidney transplantation.

Overexpression of Plasmalemmal Vesicle-Associated Protein-1 Reflects Glomerular Endothelial Injury in Cases of Proliferative Glomerulonephritis with Monoclonal IgG Deposits

Introduction

Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) occasionally presents refractory nephrotic syndrome resulting in poor renal prognosis, but its etiology is not fully elucidated. Given that glomerular endothelial cell (GEC) stress or damage may lead to podocytopathy and subsequent proteinuria, as in thrombotic microangiopathy (TMA), diabetic kidney disease, and focal segmental glomerulosclerosis, we investigated the evidence of glomerular endothelial injury by evaluating the expression of plasmalemmal vesicle-associated protein-1 (PV-1), a component of caveolae in the cases of PGNMID.

Methods

We measured the immunofluorescent PV-1 intensities of 23 PGNMID cases and compared with those of primary membranoproliferative glomerulonephritis (MPGN) (n = 5) and IgA nephropathy (IgAN) (n = 54) cases. PV-1 localization was evaluated with Caveolin-1, and CD31 staining, and the ultrastructural analysis was performed using a low-vacuum scanning electron microscope (LVSEM). To check the association of podocyte injury, we also conducted 8-oxoguanine and Wilms tumor 1 (WT1) double stain. We then evaluated PV-1 expression in other glomerulitis and glomerulopathy such as lupus nephritis and minimal change disease.

Results

The intensity of glomerular PV-1 expression in PGNMID is significantly higher than that in the other glomerular diseases, although the intensity is not associated with clinical outcomes such as urinary protein levels or renal prognosis. Immunostaining and LVSEM analysis revealed that glomerular PV-1 expression is localized in GECs in PGNMID. 8-oxoguanine accumulation was detected in WT1-positive podocytes but not in PV-1-expressing GECs, suggesting GEC-derived podocyte injury in PGNMID.

Conclusion

PV-1 overexpression reflects glomerular endothelial injury, which could be associated with podocyte oxidative stress in PGNMID cases.

Heavy Chain/Light Chain Antibody Immunofluorescence to Identify Monoclonal Plasma Cells in a Case of Plasma Cell-Rich Acute Interstitial Nephritis

Heavy/light chain (HLC) antibodies can be used to quantify intact HLC pairs. In immunofluorescence studies, they allow differentiation of monoclonal versus polyclonal immunoglobulin deposits in kidney diseases that occur in the setting of monoclonal gammopathy. Here, we present a case of a patient with acute kidney injury with first kidney biopsy suggestive of acute interstitial nephritis with a polymorphous infiltrate of plasma cells. Routine immunofluorescence did not show a monotypic plasma cell infiltrate. Serum protein electrophoresis and immunofixation revealed monoclonal immunoglobulin A (IgA) lambda. She improved with steroid therapy, but kidney function worsened after steroids were stopped. She underwent a second kidney biopsy, which showed plasma cell-rich interstitial infiltrate with a population of IgA lambda-restricted plasma cells on routine immunofluorescence. In light of this finding, Hevylite HLC antibody was used to reassess the first biopsy, which confirmed the presence of a population of plasma cells with IgA lambda restriction. Because of the presence of monotypic plasma cells, anti-CD38 monoclonal antibody (daratumumab) was initiated.

IgA vasculitis with underlying monoclonal IgA gammopathy: innovative therapeutic approach targeting plasma cells. A case series

OBJECTIVE

There is currently no evidence of the possible benefit of plasma cell-targeting therapies (PCTT) in immunoglobulin A (IgA) monoclonal gammopathy (MG) associated with IgA vasculitis (IgAV). We report the outcome of different PCTT regimens in a cohort of MG-IgAV.

METHODS

We used a French network to retrospectively describe the outcome of MG-IgAV patients treated with PCTT.

RESULTS

Five patients were included (mean age 65 years). All patients had severe baseline presentation including extensive necrotic purpura (n = 5), gastrointestinal involvement (n = 2), peripheral neuropathies (n = 2), and glomerulonephritis (n = 1). Two patients had IgA indolent multiple myeloma and three had IgA "MG of undetermined significance." Monotypic IgA deposition in the skin vessels wall was highlighted using an immunofluorescence assay. Cases of vasculitis in three patients (n = 3) were refractory to multiple line therapies, including cyclophosphamide (n = 3) or rituximab. Finally, PCTT including bortezomib plus cyclophosphamide and dexamethasone, bortezomib plus melphalan and prednisone, or bortezomib plus lenalidomide and dexamethasone were proposed, allowing complete remission in 4/5 patients without major adverse drug events.

CONCLUSION

This study suggests that the MG-IgAV phenotype might be distinctive of usual IgAV (severe and refractory to conventional immunosuppressive regimens) and supports the benefit of PCTT. This study sheds new light on the overall biology of IgAV, strengthening the pathogenic role of the monoclonal IgA component in IgAV.

The clinicopathological characteristics and outcomes of IgA nephropathy with predominant lambda or kappa light-chain deposition

PURPOSE

IgA nephropathy (IgAN) patients with monoclonal light-chain deposition may be at potential risk of hematological progression. However, whether the clinical characteristics of the patients with predominant lambda or kappa light-chain deposition were consistent with monoclonal light-chain deposition is limited to anecdotes.

METHODS

We retrospectively studied patients in whom immunofluorescence showed IgA-alone deposits (n = 617) between January 2016 and January 2020. We divided the patients into two groups, the predominant lambda or kappa light-chain deposition group and the control group. Predominant lambda or kappa light-chain deposition was defined as the deposition intensity of kappa or lambda being + - and the other deposition intensity being ≥ 2 + .

RESULTS

Nineteen patients had predominant lambda or kappa light-chain deposition. The patients had a median age of 32 years. The median proteinuria was 0.9 g/day. The median eGFR was 79.8 ml/min per 1.73 m². Two patients had a mildly abnormal FLC ratio, but serum immunofixation electrophoresis showed polyclonal immunoglobulin. Eighteen patients showed lambda light chain-dominated deposition. In electron microscopy, organized structures in dense deposits were not observed in all patients. Nine patients with proteinuria ≥ 1.0 g/day received corticosteroids and immunosuppressants. The median follow-up time was 21 months. The rate of proteinuria remission was 50%. The clinical and pathological characteristics and outcomes were not significantly different between the predominant lambda or kappa light-chain deposition group and the control group.

CONCLUSION

The result for IgAN patients with predominant kappa/lambda light-chain deposition seemed to be the same as that of IgAN patients with light-chain codeposition. However, as this was a single-center study with a small size, further multicenter studies and long-term follow-up are needed to confirm our findings.

RNA-based immunoglobulin repertoire sequencing is a new tool for the management of monoclonal gammopathy of renal (kidney) significance

The diagnostic approach of monoclonal gammopathy of renal significance is based on the detection of a monoclonal immunoglobulin in the blood and urine, and the identification of the underlying clone through bone marrow and/or peripheral blood cytologic and flow cytometry analysis. However, the monoclonal component and its corresponding clone may be undetectable using these routine techniques. Since clone identification is the cornerstone for guiding therapy and assessing disease response, more sensitive methods are required. We recently developed a high-throughput sequencing assay from bone marrow mRNA encoding immunoglobulins (RACE-RepSeq). This technique provides both full-length V(D)J region (variable, diversity and joining genes that generate unique receptors as antigen receptors) of the monoclonal immunoglobulin and the dominant immunoglobulin repertoire. This allows analysis of mutational patterns, immunoglobulin variable gene frequencies and diversity due to somatic hypermutation. Here, we evaluated the diagnostic performance of RACE-RepSeq in 16 patients with monoclonal-associated kidney lesions, and low serum monoclonal immunoglobulin and free light chain levels at diagnosis. Bone marrow immunohistochemical analysis was negative in all 11 patients so tested and 7 of 12 patients had no detectable clone matching the kidney deposits using flow cytometry analysis. By contrast, RACE-RepSeq detected a dominant clonal light chain sequence of matched isotype with respect to kidney deposits in all patients. Thus, high throughput mRNA sequencing appears highly sensitive to detect subtle clonal disorders in monoclonal gammopathy of renal significance and suggest this novel approach could help improve the management of this kidney disease.

Clinicopathological characteristics of patients with paraproteinemia and renal damage

Background

This study aimed to analyze the clinicopathological characteristics of patients with paraproteinemia and renal damage.

Methods

Ninety-six patients from 2014 to 2018 with paraproteinemia and renal damage were enrolled and the clinical data, renal pathology, treatment and prognosis data were collected.

Results

A total of 96 patients (54 male and 42 female), accounting for 2.7% of all renal biopsies, were enrolled in this study. Among them, 42 were monoclonal gammopathy of renal significance (MGRS), 21 were renal monotypic immunoglobulin alone (renal monoIg), and 19 were monoclonal gammopathy of undetermined significance (MGUS). Individuals with multiple myeloma (MM) accounted for the fewest number of patients (n  =  14). In the MGRS group, the main diseases were amyloidosis (n  =  25) and cryoglobulinemic glomerulonephritis (n  =  7), while in the MM group, the main diseases were cast nephropathy (n  =  9) and light chain deposit disease (n  =  3). In the MGUS group, it was mainly IgA nephropathy (IgAN, n  =  10) and idiopathic membranous nephropathy (n  =  5); while in the renal monoIg group, most of the cases were IgAN (n  =  19). Chemotherapy was mainly administered to patients in the MM group, while immunosuppression therapy was mostly administered to patients in the renal monoIg group. Most patients with renal monoIg exhibited a major response, followed by the patients with MGUS and MGRS, while most of the patients with MM had a partial response but none had a major response. Approximately more than half (57.1%) of the patients with MM progressed to end-stage renal disease (ESRD), followed by MGRS (33.3%); however, the mortality rate was low in both the MGRS and MM groups. The survival analysis reviewed that serum creatinine, hemoglobin levels, and the serum κ/λ ratio were independent risk factors for ESRD in patients with MGRS.

Conclusions

The clinicopathological changes in patients with MGRS were between those in patients with MM and MGUS. The treatment for MGRS and MM was more intensive, and the overall mortality rate was low. Both MGUS and renal monoIg alone exhibited slighter clinicopathological features than MGRS and MM, and the treatment was focused mostly on primary renal diseases.

Monoclonal and polyclonal immunoglobulin G deposits on tubular basement membranes of native and pretransplant kidneys: A retrospective study

Monoclonal tubular basement membrane immune deposits (TBMID) are associated with progression of interstitial injury in renal allograft. However, the significance of monoclonal and polyclonal TBMID in the native kidney remains unclear. We retrospectively analyzed 1894 native kidney biopsies and 1724 zero-hour biopsies performed between 2008 and 2018 in our institution. The rate of immunoglobulin G (IgG) TBMID was found to be 8.4% among native kidney biopsies and 0.4% among zero-hour biopsies. Polyclonal TBMID is common in IgG4-related tubulointerstitial nephritis (37.5%), diabetic nephropathy (31.3%) and lupus nephritis (25.5%). Monoclonal IgG TBMID was identified in seven cases, including three zero-hour biopsies. The combination of IgG1κ was observed in two cases, IgG1λ in three, and IgG2κ in two. Electron microscopy revealed powdery electron-dense deposits in all cases. Monoclonal gammopathy of undetermined significance was diagnosed in one case. Although one patient with focal segmental glomerulosclerosis developed renal failure, all others exhibited stable renal function. Monoclonal IgG TBMID in the native kidney is not associated with renal prognosis. However, this may be an interesting immunopathological finding that would help clarify the pathogenesis of TBM immune deposits. Further study for both monoclonal and polyclonal TBMID is required in the future.

Clinicopathological significance of light chain deposition in IgA nephropathy

BACKGROUND

Clinicopathological significance of light chain deposition in IgA nephropathy and the relation of monotypic IgA deposition to bone marrow abnormalities are important issues to be clarified.

METHODS

We retrospectively investigated light chain deposition in 526 patients with IgA nephropathy. We divided the patients into 5 groups according to the balance of intensity of both light chain deposition: lambda monotypic, lambda dominant, polytypic, kappa dominant and kappa monotypic. Clinicopathological parameters were compared among the groups. The relation of monotypic IgA deposition to hematological malignancy was also evaluated.

RESULTS

The prevalence of monotypic IgA deposition was 6.3%, 33 patients (21 lambda and 12 kappa). Thirty-two (4.0%) and 10 patients (1.9%) were classified into lambda and kappa dominant groups, respectively. Polytypic IgA deposition was observed in 455 patients (85.7%). Age of onset, age at biopsy, urinary protein creatinine ratio, the percentage of global glomerulosclerosis, and the degree of IgA and C3 deposition were different among the groups. However, there was no gradual difference according to the groups. No patient with monotypic IgA deposition showed hematological abnormality at biopsy and during follow-up.

CONCLUSIONS

The prevalence of IgA monotypic deposition was extremely low. Clinicopathologically, we could not differentiate patients with monotypic IgA deposition from those with polytypic one and no hematological disorder was documented in patients with monotypic IgA deposition. Whether IgA nephropathy with monotypic IgA deposition and that with polytypic one is the same entity or not, and relation between monotypic IgA deposition and hematological malignancy should be clarified by further investigations.

Results of a nation-wide cohort study suggest favorable long-term outcomes of clone-targeted chemotherapy in immunotactoid glomerulopathy

Immunotactoid glomerulopathy is a rare disease defined by glomerular microtubular immunoglobulin deposits. Since management and long-term outcomes remain poorly described, we retrospectively analyzed results of 27 adults from 21 departments of nephrology in France accrued over 19 years. Inclusion criteria were presence of glomerular Congo red-negative monotypic immunoglobulin deposits with ultrastructural microtubular organization, without evidence for cryoglobulinemic glomerulonephritis. Baseline manifestations of this cohort included: proteinuria (median 6.0 g/day), nephrotic syndrome (70%), microscopic hematuria (74%) and hypertension (56%) with a median serum creatinine of 1.5 mg/dL. Nineteen patients had detectable serum and/or urine monoclonal gammopathy. A bone marrow and/or peripheral blood clonal disorder was identified in 18 cases (16 lymphocytic and 2 plasmacytic disorders). Hematologic diagnosis was chronic/small lymphocytic lymphoma in 13, and monoclonal gammopathy of renal significance in 14 cases. Kidney biopsy showed atypical membranous in 16 or membranoproliferative glomerulonephritis in 11 cases, with microtubular monotypic IgG deposits (kappa in 17 of 27 cases), most commonly IgG1. Identical intracytoplasmic microtubules were observed in clonal lymphocytes from 5 of 10 tested patients. Among 21 patients who received alkylating agents, rituximab-based or bortezomib-based chemotherapy, 18 achieved a kidney response. After a median follow-up of 40 months, 16 patients had sustained kidney response, 7 had reached end-stage kidney disease, and 6 died. Chronic/small lymphocytic lymphoma appears as a common underlying condition in immunotactoid glomerulopathy, but clonal detection remains inconstant with routine techniques in patients with monoclonal gammopathy of renal significance. Thus, early diagnosis and hematological response after clone-targeted chemotherapy was associated with favorable outcomes. Hence, thorough pathologic and hematologic workup is key to the management of immunotactoid glomerulopathy.

A case of proliferative glomerulonephritis with immunoglobulin A1-lambda deposits successfully treated by chemotherapy

A 74-year-old man presented with nephrotic syndrome and kidney insufficiency. Laboratory tests revealed monoclonal gammopathy of immunoglobulin A-lambda. Renal biopsy revealed diffuse mesangial proliferation and double-contoured basement membranes. Immunofluorescent analyses showed granular deposition of immunoglobulin A and C3 at the capillary walls and mesangial regions. Immunohistochemistry suggested monoclonal deposition of immunoglobulin A1-lambda. Electron microscopic analyses showed finely granular electron-dense deposits at mesangial and subendothelial areas. These findings suggested immunoglobulin A-type proliferative glomerulonephritis with monoclonal immunoglobulin deposits. Based on the results of bone marrow aspiration, multiple myeloma was diagnosed. Because the renal manifestation was considered to be affected by monoclonal gammopathy, chemotherapy was initiated rather than immunomodulatory therapy. Although bortezomib and dexamethasone proved ineffective, second chemotherapy with elotuzumab, lenalidomide, and dexamethasone was successful, and kidney function recovered. Effective treatments for proliferative glomerulonephritis with monoclonal immunoglobulin deposits have not been established. This represents the first description of a patient successfully treated for proliferative glomerulonephritis with monoclonal immunoglobulin deposits by chemotherapy using elotuzumab.

The clinical implication of monoclonal gammopathies: monoclonal gammopathy of undetermined significance and of renal significance

Monoclonal gammopathy of renal significance (MGRS) has introduced a new perspective to several well-known disease entities impacting nephrology, haematology and pathology. Given the constantly changing disease spectrum of these entities, it is clinically imperative to establish diagnostic and treatment pathways supported by evidence-based medicine. MGRS is a disease of the kidney, secondary to plasma cell clonal proliferation or immune dysfunction, requiring therapeutic intervention to eradicate the offending clone. To fully understand the disease(s), it is prerequisite to determine the significance of the findings. The diagnostic work up should be extensive due to the wide heterogeneity of clinical presentation, ultimately necessitating kidney biopsy. Particular patient profiles such as AL amyloidosis, which may be diagnosed through biopsies of other tissues/organs, may be an exception. Treatment decisions should be formulated by multi-disciplinary consensus: nephrologists, haematologists and pathologists. The ultimate goal in managing MGRS is eradication of the offending plasma cell clone which requires targeted chemotherapy and, in eligible cases, haematopoietic stem cell transplantation. We present a review of diagnostic procedures, treatment options and advances in the last few years in the management of MGRS in an effort to acquaint specialists with this new face of several older diseases.

Monoclonal immunoglobulin G deposits on tubular basement membrane in renal allograft: is this significant for chronic allograft injury?

Background

Tubular basement membrane immune deposits (TBMID) has rarely been observed in renal allografts. It is usually found in BK virus nephropathy and immune complex glomerulonephritis; however, its significance is not well understood. We conducted a retrospective clinicopathological study on monoclonal immunoglobulin G (IgG) TBMID.

Methods

We studied 7177 renal allograft biopsy specimens obtained from Tokyo Women’s Medical University from 2007 to 2015 and performed light microscopic, electron microscopic and immunofluorescence studies.

Results

Tubular basement membrane (TBM) deposits of IgG were found in 73 biopsies from 61 patients and the IgG subclass was obtained in 31 biopsies. There were no cases of monoclonal IgA or IgM TBMID. In total, 13 biopsies from 10 patients showed monoclonal IgG TBMID. Of these, seven showed monoclonal IgG1κ TBMID and one each showed monoclonal IgG2κ, IgG2λ and IgG3κ TBMID. Conversely, eight patients showed polyclonal IgG TBMID. In electron microscopy, large granular electron-dense deposits (EDDs) in the TBM were detected in all patients with monoclonal IgG1κ TBMID. EDDs were absent in TBM in patients with monoclonal IgG2κ, IgG2λ or IgG3κ TBMID. Progression of interstitial fibrosis and tubular atrophy (IFTA) was significantly higher in patients with monoclonal IgG1κ TBMID than in those with polyclonal IgG TBMID (P < 0.05). There were no significant differences in the other clinical parameters between monoclonal IgG1κ and polyclonal IgG TBMID.

Conclusions

This is the first study of patients with monoclonal IgG TBMID in renal allografts. We found that monoclonal IgG1κ TBMID was associated with EDD formation in TBM and IFTA progression.

Management and treatment of glomerular diseases (part 2): conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

In November 2017, the Kidney Disease: Improving Global Outcomes (KDIGO) initiative brought a diverse panel of experts in glomerular diseases together to discuss the 2012 KDIGO glomerulonephritis guideline in the context of new developments and insights that had occurred over the years since its publication. During this KDIGO Controversies Conference on Glomerular Diseases, the group examined data on disease pathogenesis, biomarkers, and treatments to identify areas of consensus and areas of controversy. This report summarizes the discussions on primary podocytopathies, lupus nephritis, anti-neutrophil cytoplasmic antibody-associated nephritis, complement-mediated kidney diseases, and monoclonal gammopathies of renal significance.

IgA plasma cell neoplasms are characterized by poorer long-term survival and increased genomic complexity compared to IgG neoplasms

The characteristics of the IgA plasma cell neoplasms are not clearly reported in the literature. The main goal of this study is to examine IgA plasma cell neoplasms (PCN) and to compare them to IgG lesions. After at least 5 years from the identification of an M protein, 98 cases were selected, the presentation and clinical evolution of 45 IgA neoplasms were compared to 43 cases of IgG gammopathies. The classification at presentation as monoclonal gammopathy of undermined significance (MGUS)-22 of 45 IgA and 20 of 43 IgG (49 vs 46%), plasma cell myeloma (PCM)-22 of 45 IgA and 22 of 43 IgG (49 vs 51%) and smoldering PCM (SPCM)-1 each (2% for both) was essentially identical. No solitary plasmacytomas were identified. At presentation, IgA patients were younger (66.5 ± 11.3 vs. 69.2 ± 10.7 years), less likely to have bone lesions (12/45 vs 18/43, p < 0.14) or immunoparesis (51% vs. 63%), differences statistically insignificant. Cases with normal fluorescence in-situ hybridization (FISH) results, 27% for IgA vs 61% for IgG (p < 0.037) were statistically different. The IgA patients had worse survival (80 vs 108 months median IgA vs IgG, p < 0.013), difference not detectable in the first 5 years, but substantial after 10. In conclusion, poorer long-term survival and increased genomic complexity by FISH are characteristics of IgA PCNs.

The evaluation of monoclonal gammopathy of renal significance: a consensus report of the International Kidney and Monoclonal Gammopathy Research Group

The term monoclonal gammopathy of renal significance (MGRS) was introduced by the International Kidney and Monoclonal Gammopathy Research Group (IKMG) in 2012. The IKMG met in April 2017 to refine the definition of MGRS and to update the diagnostic criteria for MGRS-related diseases. Accordingly, in this Expert Consensus Document, the IKMG redefines MGRS as a clonal proliferative disorder that produces a nephrotoxic monoclonal immunoglobulin and does not meet previously defined haematological criteria for treatment of a specific malignancy. The diagnosis of MGRS-related disease is established by kidney biopsy and immunofluorescence studies to identify the monotypic immunoglobulin deposits (although these deposits are minimal in patients with either C3 glomerulopathy or thrombotic microangiopathy). Accordingly, the IKMG recommends a kidney biopsy in patients suspected of having MGRS to maximize the chance of correct diagnosis. Serum and urine protein electrophoresis and immunofixation, as well as analyses of serum free light chains, should also be performed to identify the monoclonal immunoglobulin, which helps to establish the diagnosis of MGRS and might also be useful for assessing responses to treatment. Finally, bone marrow aspiration and biopsy should be conducted to identify the lymphoproliferative clone. Flow cytometry can be helpful in identifying small clones. Additional genetic tests and fluorescent in situ hybridization studies are helpful for clonal identification and for generating treatment recommendations. Treatment of MGRS was not addressed at the 2017 IKMG meeting; consequently, this Expert Consensus Document does not include any recommendations for the treatment of patients with MGRS.

This Expert Consensus Document from the International Kidney and Monoclonal Gammopathy Research Group includes an updated definition of monoclonal gammopathy of renal significance (MGRS) and recommendations for the use of kidney biopsy and other modalities for evaluating suspected MGRS

Light chain only variant of proliferative glomerulonephritis with monoclonal immunoglobulin deposits is associated with a high detection rate of the pathogenic plasma cell clone

IgG (mainly IgG3) is the most commonly involved isotype in proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID). Here we describe the first series of PGNMID with deposition of monoclonal immunoglobulin light chain only (PGNMID-light chain). This multicenter cohort of 17 patients presented with nephritic or nephrotic syndrome with underlying hematologic conditions of monoclonal gammopathy of renal significance (71%) or multiple myeloma (29%). Monoclonal immunoglobulin was identified by serum and urine immunofixation in 65% and 73%, respectively, with abnormal serum free light chain in 83%, and a detectable bone marrow plasma cell clone in 88% of patients. Renal biopsy showed a membranoproliferative pattern in most patients. By immunofluorescence, deposits were restricted to glomeruli and composed of restricted light chain (kappa in 71%) and C3, with granular appearance and subendothelial, mesangial and subepithelial distribution by electron microscopy. Proteomic analysis in four cases of kappa PGNMID-light chain revealed spectra for kappa constant and variable domains, without evidence of Ig heavy chains; spectra for proteins of the alternative pathway of complement and terminal complex were detected in three. The classical pathway was not detected in three cases. After median follow up of 70 months, the renal response was dependent on a hematologic response and occurred in six of ten patients treated with plasma cell-directed chemotherapy but none of five patients receiving other therapies. Thus, PGNMID-light chain differs from PGNMID-IgG by higher frequency of a detectable pathogenic plasma cell clone. Hence, proper recognition is crucial as anti-myeloma agents may improve renal prognosis. Activation of an alternative pathway of complement by monoclonal immunoglobulin light chain likely plays a role in its pathogenesis.

Successful treatment with steroid and cyclosporine A in a patient with immunoglobulin A-proliferative glomerulonephritis with monoclonal immunoglobulin deposits

We report a case of glomerulonephritis with monoclonal immunoglobulin (Ig) A deposits as a form of monoclonal gammopathy of renal significance (MGRS) caused by monoclonal immunoglobulins without blood disorders in a 41-year-old woman. She developed lower leg oedema and was hospitalized because of nephrotic syndrome. Serum and urine were negative for M protein, and the free light chain κ/λ ratio was within the normal range. Renal histopathological findings included mesangial proliferation, endocapillary cell proliferation, and a double-contour appearance of the capillary walls. Immunofluorescent staining indicated IgA and C3 deposits on the mesangium and capillary walls. Only λ chain and IgA1 deposits were noted. Fine granular sub-endothelial deposits with no specific structure were observed under electron microscopy. The patient was diagnosed with IgA-proliferative glomerulonephritis with monoclonal immunoglobulin deposits (IgA-PGNMID). The patient had decreased urine protein and sediment erythrocytes after she underwent two rounds of steroid pulse therapy and oral steroid therapy, but proteinuria and haematuria still remained. Four months later, the patient was administered 50 mg/day cyclosporine (CsA), and proteinuria and haematuria dramatically decreased. Only a few case reports have been published on IgA-PGNMID. This case is rare in that the patient achieved successful treatment using a combination of steroids and CsA.

Proliferative glomerulonephritis with monoclonal IgG deposits in children and young adults

BACKGROUND

Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) has been recognized as a distinct entity in recent years. To the best of our knowledge, all patients with PGNMID reported thus far were older than 20 years of age. We now report five cases of PGNMID in patients under 20 years of age.

METHODS

The clinical database was searched for patients with native kidney biopsies from 9/2011 to 8/2017, and cases with a diagnosis of PGNMID were retrieved. Light microscopy specimens and immunofluorescence and electron microscopy images were revisited. Clinical data and kidney biopsy findings for patients under the age of 20 were recorded.

RESULTS

Five (0.78%) of a total of 637 patients younger than 20 with native renal biopsies had a diagnosis of PGNMID, including three males and two females with an average age of 14 years old (range 10-19). All five patients presented with microscopic hematuria and proteinuria. Three patients were nephrotic and their C3 levels were low. All five cases showed a membranoproliferative pattern with abundant mesangial and subendothelial monoclonal IgG3 deposits (3 κ and 2 λ light chain, respectively). The patients were followed up to 56 months. Two patients had re-biopsies 28 and 18 months after initial diagnosis and both showed similar morphologic changes. Various treatments were attempted including prednisone, mycophenolate mofetil, tacrolimus, rituximab, and eculizmab, with mixed responses.

CONCLUSIONS

PGNMID does occur in children and young adults. Membranoproliferative glomerulonephritis pattern with monoclonal IgG3 deposits is a common feature. Despite various immunosuppressive treatments, the disease appears slowly progressive.

Staphylococcal Infection-Related Glomerulonephritis With Cryoglobulinemic Features

Introduction

Staphylococcal infection–related glomerulonephritis (GN) has been shown to represent a unique form of infection-related GN that contains IgA-dominant deposits and is often seen concurrently with the bacterial infection. Biopsies commonly reveal an endocapillary proliferative and/or exudative or mesangial proliferative GN. Rare cases have been reported to show cryoglobulin-like features, including hyaline pseudothrombi and wireloop deposits; however, detailed characterization of these cases is lacking.

Methods

The pathology archives from the University of Utah and Sharp Memorial Hospital were reviewed from January 2016 to September 2017 in search of cases with GN containing IgA-dominant deposits and features of cryoglobulinemia.

Results

Of 1965 native kidney biopsies, 5 showed IgA-dominant GN with cryoglobulinemic features. All patients had active staphylococcal infections at the time of biopsy. All presented with acute kidney injury (serum creatinine range: 1.7−6 mg/dl), and all had proteinuria and hematuria. All biopsies showed exudative GN, and 4 biopsies had focal crescents. All had focally prominent hyaline pseudothrombi with or without wireloop deposits, and all showed co-dominant staining for IgA and C3 on immunofluorescence microscopy. Serologic testing for cryoglobulinemia was performed in 3 patients and was transiently positive in 1 patient. Four patients required hemodialysis at last follow-up, whereas 1 patient returned to baseline kidney function.

Conclusion

IgA-dominant GN with cryoglobulinemic features is an uncommon but severe form of glomerular injury in patients with staphylococcal infections. Four of 5 patients had crescentic glomerular injuries, all of whom required hemodialysis at last follow-up. Patients with IgA-dominant GN with features of cryoglobulinemia should be evaluated for active staphylococcal infection.

The Complexity and Heterogeneity of Monoclonal Immunoglobulin-Associated Renal Diseases

Monoclonal gammopathies are characterized by the overproduction of monoclonal Ig (MIg) detectable in the serum or urine resulting from a clonal proliferation of plasma cells or B lymphocytes. The underlying hematologic conditions range from malignant neoplasms of plasma cells or B lymphocytes, including multiple myeloma and B-cell lymphoproliferative disorders, to nonmalignant small clonal proliferations. The term MGUS implies presence of an MIg in the setting of a "benign" hematologic condition without renal or other end organ damage. The term MGRS was recently introduced to indicate monoclonal gammopathy with MIg-associated renal disease in the absence of hematologic malignancy. Most MIg-associated renal diseases result from the direct deposition of nephrotoxic MIg or its light- or heavy-chain fragments in various renal tissue compartments. Immunofluorescence microscopy is essential to identify the offending MIg and define its tissue distribution. Mass spectrometry is helpful in difficult cases. Conditions caused by direct tissue deposition of MIg include common disorders, such as cast nephropathy, amyloidosis, and MIg deposition diseases, as well as uncommon disorders, such as immunotactoid glomerulopathy, proliferative GN with MIg deposits, light-chain proximal tubulopathy, and the rare entities of crystal-storing histiocytosis and crystalglobulinemia. Indirect mechanisms of MIg-induced renal disease can cause C3 glomerulopathy or thrombotic microangiopathy without tissue MIg deposits. Treatment of MIg-associated renal disease is aimed at eliminating the clonal plasma cell or B-cell population as appropriate. Both the renal and the underlying hematologic disorders influence the management and prognosis of MIg-associated renal diseases.

[IgA nephropathy: Unusual forms]

IgA nephropathy can have various initial presentation and evolutive characteristics. In this article, specific forms of IgA nephropathy are described, such as hypertensive emergency, nephrotic syndrome, rapidly progressive glomerulonephritis, monotypic IgA deposits, or IgA nephropathy associated with inflammatory diseases. Identification of these specific forms is needed to better characterize and treat these rare pathologies.

Monoclonal gammopathy of renal significance (MGRS) increases the risk for progression to multiple myeloma: an observational study of 2935 MGUS patients

Purpose

Monoclonal gammopathy of undetermined significance (MGUS) is a premalignancy preceding multiple myeloma (MM) or related disorders. In MGUS, renal impairment caused by deposition of the monoclonal immunoglobulins or free light-chains monoclonal gammopathy of renal significance (MGRS) is often associated with high morbidity and mortality. We analysed the prevalence of renal impairment, clinical features and the long-term outcome in 2935 patients with MGUS.

Methods

Between 1/2000 and 8/2016, 2935 adult patients with MGUS were identified in our database.

Results

In 44/2935 (1.5%) patients MGRS was diagnosed. In MGRS patients, significantly more progressions to MM were observed than in MGUS patients (18% vs. 3%; P<0.001). MGRS patients showed a higher risk for progression (HR 3.3 [1.5-7.4]) in the Cox model. Median time to progression was 23 years for MGUS and 18.8 years for MGRS patients. Corresponding progression rate was 8.8 [7.2-10.7] per 1000 patient-years (py) for MGUS patients and 30.6 [15.3–61] for the MGRS group. Risk for progression within the first year after diagnosis was 1% [0.6-1.4] in the MGUS group and 10% [4-29] among MGRS patients.

Conclusion

The significantly higher risk for progression to MM means MGRS patients should be monitored carefully and treated in a specialized centre.