Promising response of proliferative glomerulonephritis with monoclonal IgG deposits to low-dose daratumumab: a case report

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) is a rare disease without standardized treatment modalities. Daratumumab is a human IgG monoclonal anti-CD38 antibody that has been demonstrated to be highly effective and safe in the treatment of PGNMID. This article reports a 66-year-old female who suffered from edema in both lower limbs and face for 6 years with mild proteinuria and hypoproteinemia. Renal biopsy displayed eight glomeruli, among which two presented with glomerulosclerosis, and the remaining six exhibited moderate diffuse hyperplasia of glomerular mesangial cells and stroma with endothelial cell proliferation. Immunofluorescence microscopy revealed lumpy and diffuse deposits of C3, C1q, IgG, and κ light chain in the glomerular mesangium, with strongly positive staining for IgG3 and varying degrees of weak to negative staining for IgG1, IgG2, IgG4, and λ light chain. Additionally, ultrastructural analysis unveiled that the glomerular basement membrane was segmentally thickened, accompanied by diffuse pedicle fusion, segmental tethered insertion, subendothelial deposits, and electron-dense material in tethered areas. The patient received a total dose of 800 mg of daratumumab (400 mg daily for two consecutive days), as well as daily prednisone (25 mg) and valsartan (80 mg), for treatment and achieved complete remission after three-month follow-up. This case represents an early attempt to treat PGNMID with low-dose daratumumab but requires long-term follow-up.

Light chain only variant of proliferative glomerulonephritis with monoclonal immunoglobulin deposits: a clinicopathological study of three cases

AIMS

To explore the clinical and pathological features of light chain only variant of proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID-LC).

METHODS

From January 2010 to December 2022, patients who were diagnosed with PGNMID-LC were selected, and their clinical and pathological features were retrospectively analysed.

RESULTS

Three males aged 42-61 years old were enrolled. Hypertension was present in three patients, oedema in three patients, anaemia in two patients, proteinuria in three patients, nephrotic syndrome in one patient, microscopic haematuria in three patients, renal insufficiency in two patients and hypocomplementaemia of C3 in one patient. Elevated serum-free LC ratios and plasmacytosis on bone marrow smears were observed in three patients, and κ was identified by serum protein immunofixation electrophoresis in one patient. Renal biopsy showed membranoproliferative glomerulonephritis in two patients and endocapillary proliferative glomerulonephritis in one patient on light microscopy. Immunofluorescence indicated restricted κ LC and C3 distributed in glomeruli. By electron microscopy, electron-dense deposits without substructure were identified predominantly in the mesangial and subendothelial regions and were variable in the subepithelial region. Two patients were treated with plasma cell-directed chemotherapy and achieved haematological complete response or very good partial response, and one of them achieved a renal status of complete remission. One patient treated with immunosuppressive therapy only did not achieve haematological or renal remission.

CONCLUSIONS

PGNMID-LC is a rare and uniform disease with a high frequency of a detectable pathogenic plasma cell clone and is characterised by glomerular deposition of restricted LC and C3 in renal pathology. Plasma cell-directed chemotherapy may improve haematological and renal prognosis.

Paraprotein-Mediated Glomerular Diseases

Paraproteinemias are a group of complex diseases associated with an overproduction of a monoclonal immunoglobulin that can cause a diversity of kidney disorders and end-organ damage. In this review, we focus on paraprotein-mediated glomerular diseases. Kidney biopsy plays a crucial role in diagnosing these disorders, enabling the identification of specific histological patterns. These lesions are categorized into organized (such as amyloidosis, immunotactoid glomerulopathy, fibrillary glomerulonephritis, cryoglobulinemic glomerulonephritis, and monoclonal crystalline glomerulopathies) and nonorganized deposits (such as monoclonal Ig deposition disease and proliferative glomerulonephritis with monoclonal Ig deposits) based on the characteristics of immunofluorescence findings and the ultrastructural appearance of deposits on electron microscopy. This review aims to provide an update, highlight, and discuss clinicopathological aspects such as definition, epidemiology, clinical manifestations, mechanisms of kidney injury, histological features, and diagnostic procedures.

Proliferative glomerulonephritis with monoclonal IgG deposits in an adolescent successfully treated with daratumumab

There is no specific treatment for proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID), a disease that is very rare in the pediatric population. We report the case of a 15-year-old boy who presented with mildly reduced kidney function and nephrotic syndrome. Kidney biopsy revealed PGNMID with monoclonal deposits of IgG3 with kappa light chain restriction. Flow cytometry showed a significant CD38 plasma cell population in the peripheral blood in the absence of other signs of hematological malignancy. The patient was treated with a 6-month course of daratumumab, a monoclonal antibody targeting CD38. There was a significant reduction in proteinuria and normalization of kidney function. Based on positive experience with adults, daratumumab should also be studied in children with PGNMID.

Double Hit of Hydroxichloroquine and Amiodarone Induced Renal Phospholipidosis in a Patient with Monoclonal Gammopathy and Sclerodermiform Syndrome: A Case Report and Review of the Literature

Phospholipidosis is a rare disorder which consists of an excessive intracellular accumulation of phospholipids and the appearance of zebra bodies or lamellar bodies when looking at them using electron microscopy. This disease is associated with certain genetic diseases or is secondary to drugs or toxins. Drug-induced phospholipidosis encompasses many types of pharmaceuticals, most notably chloroquine, amiodarone or ciprofloxacin. Clinically and histologically, renal involvement can be highly variable, with the diagnosis not being made until the zebra bodies are seen under an electron microscope. These findings may require genetic testing to discount Fabry disease, as its histological findings are indistinguishable. Most of the chemicals responsible are cationic amphiphilic drugs, and several mechanisms have been hypothesized for the formation of zebra bodies and their pathogenic significance. However, the relationship between drug toxicity and phospholipid accumulation, zebra bodies and organ dysfunction remains enigmatic, as do the renal consequences of drug withdrawal. We present, to our knowledge, the first case report of acute renal injury with a monoclonal gammopathy of renal significance, lesions, and sclerodermiform syndrome, with zebra bodies that were associated with the initiation of a hydroxychloroquine and amiodarone treatment, as an example of drug-induced-phospholipidosis.

IgM kappa proliferative glomerulonephritis with monoclonal immunoglobulin deposition complicated with nocardiosis dermatitis: a case report and review of literature

Rationale

Monoclonal gammopathy of renal significance (MGRS) represents a group of disorders caused by monoclonal immunoglobulin (M protein) secreted by B cells or plasma cells. Proliferative glomerulonephritis with monoclonal immunoglobulin deposition (PGNMID) is a glomerular disease and a form of MGRS. Here, we presented a rare case of a patient with IgM kappa PGNMID complicated with nocardiosis dermatitis.

Patient concerns and diagnoses

A 56-year-old man was admitted to the hospital because of cutaneous purpura and proteinuria. His initial pathological diagnosis indicated membranous proliferative glomerulonephritis, IgM(++), and subacute interstitial nephritis. Based on further examination, he was finally diagnosed to have IgM kappa PGNMID and subacute interstitial nephritis. After the initial diagnosis, the patient received hormonal therapy. During the treatment, nocardiosis dermatitis emerged as a complication, and the hormonal therapy was gradually reduced. The patient refused further treatment with rituximab, and his health is currently stable.

Outcomes

IgM kappa PGNMID complicated with nocardiosis dermatitis is an extremely rare occurrence. Laboratory examination and pathological analysis are required to confirm the diagnosis of this disorder. Timely and accurate diagnosis is essential for the appropriate treatment of PGNMID.

The Role of Bone Marrow Biopsy Evaluation in the Workup for Monoclonal Gammopathy of Renal Significance: A Diagnosis of Exclusion

CONTEXT.—

Monoclonal gammopathy of renal significance (MGRS) is a relatively new concept for patients with renal monoclonal protein deposition (RMPD) (except monoclonal cast nephropathy) and has been used as a reason for nephrologists to obtain a bone marrow biopsy (BMB). It takes a team of pathologists and clinicians to determine when RMPD at our institution can be defined as MGRS.

OBJECTIVE.—

To identify the proportion of various subtypes of tentative MGRS diagnosed by renal biopsy that can be confirmed as final MGRS after BMB.

DESIGN.—

One hundred thirty kidney biopsies with variants of RMPD were identified during the past 10 years. Biopsy cases with known myeloma, B-cell lymphoma, or monoclonal cast nephropathy were separated as a heavy-burden group. The remaining biopsies with RMPD were considered tentative MGRS. Their BMB and clinical indices were further analyzed to determine the final percentage of MGRS diagnoses.

RESULTS.—

Among the 130 renal paraprotein deposition cases, 44 (33.8%) were categorized as the heavy-burden group. In the remaining 86 cases, 33 (38.4%) with subsequent identification of myeloma (>10% of monoclonal plasma cells) or lymphoma in BMB were further considered as heavy-burden cases. Eighteen cases (18 of 86; 20.9%) did not receive follow-up BMB; thus, no further analysis was performed. BMBs diagnosed as either nonmalignant (no plasma cells; 8 of 86 cases; 9.3%) or premalignant (<10% plasma cells; 27 of 86 cases; 31.4%) were confirmed to be final MGRS (35 of 86; 40.7%).

CONCLUSIONS.—

The data indicate that BMB is an important element in the confirmation of MGRS.

Proliferative Glomerulonephritis With Monoclonal IgG Deposits: Another Unusual Presentation

Proliferative glomerulonephritis with monoclonal immunoglobulin G (IgG) deposits (PGNMID) is a relatively rare diagnosis with variable presentation. When detectable, the disease is typically indolent rather than malignant and recurs in transplant cases. Here, we report a case of PGNMID, which presented clinically as rapidly progressive glomerulonephritis (RPGN). The patient presented to his primary care physician's office with diarrhea for one day and was admitted for acute kidney injury. Urine sediment was active, and the patient had nephrotic range proteinuria. Serologic workup was negative for any monoclonality: ANA, c-ANCA, and p-ANCA. Kidney biopsy showed diffuse proliferative and crescentic glomerulonephritis with IgG3-kappa restricted deposits, consistent with PGNMID. The patient required dialysis initiation, and corticosteroids were administered. The patient declined further immunomodulatory treatment and remains hemodialysis-dependent. This case highlights the potential for severe renal damage from monoclonal proteins despite an indolent or even undetectable hematologic clone. This entity needs further studies to better understand its immuno-physiological background and develop a standard treatment regimen.

Systematic review and meta-analysis of the clinical features of MGRS

BACKGROUND

It is crucial to identify patients with monoclonal gammopathy of renal significance (MGRS) from those without MGRS but with monoclonal gammopathy and concomitant kidney diseases. However, there have been few studies with large sample sizes, and their findings were inconsistent. This study aimed to conduct a meta-analysis of MGRS to describe the general characteristics of MGRS and its predictive factors.

METHODS

Cohort or case-control studies published through December 2022 and related to clinicopathological features of MGRS were retrieved from the PubMed, Cochrane Library, Web of Science, Scopus, and Embase databases. Two researchers searched for studies that met the inclusion criteria. In the univariate analysis, fixed- or random- effects models were used to obtain pooled estimates of the weighted mean difference (WMD) and odds ratio (OR) for risk factors. In the multivariate analysis, the ORs of the independent risk factors from each study were pooled after transforming the original estimates.

RESULTS

The meta-analysis included six studies. Univariate analysis showed that the following variables were statistically significant in MGRS: age (WMD = 1.78, 95%CI 0.21-3.35), hypertension (OR = 0.54, 95%CI 0.4-0.73), diabetes (OR = 0.42, 95%CI 0.29-0.59), albumin (WMD = - 0.26, 95%CI - 0.38--0.14), urinary protein level (WMD = 0.76, 95%CI 0.31-1.2), urinary protein ≥ 1.5 g/d (OR = 1.98, 95%CI 1.46-2.68), lambda-chain value (WMD = 29.02, 95%CI 16.55-41.49), abnormal free light-chain ratio (OR = 4.16, 95%CI 1.65-10.47), bone marrow puncture rate (OR = 5.11, 95% CI 1.31-19.95), and abnormal bone marrow outcome rate (OR = 9.63, 95%CI 1.98-46.88). Multivariate analysis showed urinary protein ≥ 1.5 g/d (OR = 2.80, 95%CI 1.53-5.15) and an abnormal free light-chain ratio (OR = 6.98, 95%CI 4.10-11.91) were associated with predictors of MGRS.

CONCLUSIONS

Compared with non-MGRS patients with monoclonal gammopathy and concomitant kidney diseases, patients with MGRS were older, had fewer underlying diseases, more urinary protein, more abnormal free light-chain ratio, and more abnormal bone marrow results. Urinary protein ≥ 1.5 g/d and an abnormal free light-chain ratio were independent risk factors for MGRS.

Kidney Transplantation in Multiple Myeloma and Monoclonal Gammopathy of Renal Significance

Recent advances in the treatment of plasma cell disorders (PCDs) have provided a wealth of therapy alternatives and improved overall survival tremendously. Various types of PCDs are associated with kidney injury and end-stage kidney disease in a considerable number of patients. Kidney transplantation (KTx) is the best option for renal replacement therapy in select patients in terms of both quality of life parameters and overall survival. Even with modern therapies, all PCDs carry the risk of hematologic progression, whereas histologic recurrence and graft loss are other prevailing concerns in these patients. The risk of mortality is also higher in some of these disorders compared with KTx recipients who suffer from other causes of kidney disease. Unlike solid cancers, there is no well-defined "waiting time" after hematologic remission before proceeding to KTx. Thus, clinicians are usually reluctant to recommend KTx to patients who develop end-stage kidney disease due to PCDs. This review aims to provide the current evidence on KTx outcomes in patients with monoclonal gammopathy of renal significance and multiple myeloma. Although immunoglobulin light chain amyloidosis is a monoclonal gammopathy of renal significance subtype, KTx outcomes in this group are mentioned in another chapter of this issue.

Characteristics of Complement Protein Deposition in Proliferative Glomerulonephritis with Monoclonal Immunoglobulin Deposition

BACKGROUND

Hypocomplementemia and complement co-deposition with monoclonal immunoglobulins in glomeruli are not rare in proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID). Deposition of monoclonal immunoglobulins in glomeruli has been suggested to activate complement and cause kidney injury. However, the profiles of complement activation in PGNMID and their clinical and pathologic significance need to be clarified.

METHODS

Forty-six patients with PGNMID were enrolled. Proteomic analysis of glomeruli using laser microdissection and mass spectrometry was performed for ten patients with PGNMID to determine the composition of glomerular deposits. Kidney deposition of complement components was detected by immunohistochemistry and immunofluorescence. Urinary and plasma levels of complement components were measured by an enzyme-linked immunosorbent assay. Group differences were assessed using t tests or Mann-Whitney U tests depending on the distribution. Correlation analysis was performed using Spearman rank correlation or Pearson correlation.

RESULTS

Laser microdissection and mass spectrometry-based proteomic analysis showed that complement components were the most enriched proteins deposited in the glomeruli of patients with PGNMID. Glomerular deposition of C3c, C4d, and C5b-9 was detected in most patients. Levels of urinary and plasma C3a, C5a, soluble C5b-9, C4d, Bb, and C1q as well as urinary mannose-binding lectin were significantly higher in patients with PGNMID compared with healthy controls. The intensity of C3c and C4d deposition in glomeruli correlated with serum creatinine and the percentage of crescents, respectively. Furthermore, levels of urinary complement components correlated positively with serum creatinine, urinary protein excretion, percentage of crescents, and global glomerulosclerosis in kidney biopsies, whereas plasma levels of most complement components did not show a significant correlation with clinicopathologic parameters. In multivariable analysis, a higher level of urinary C4d was identified as an independent risk factor of kidney failure.

CONCLUSIONS

The complement system was found to be overactivated in PGNMID, and levels of urinary complements correlated with disease severity. A higher level of urinary C4d was identified as an independent risk factor of kidney failure.

Post-Transplant Monoclonal Gammopathy of Renal Significance: A Case Report

The term monoclonal gammopathy of renal significance has been used to classify the presence of a monoclonal gammopathy or lymphoproliferative disorders that do not meet hematological criteria for myeloma but instead cause kidney damage. Mostly, post-transplant monoclonal gammopathy of renal significance occurs due to recurrent disease. In contrast, the incidence of de novo post-transplant monoclonal gammopathy of renal significance has not been established, as it is considered a rare disease, presenting a unique challenge in terms of diagnosis, management, and potential impact on graft survival. Here, we report a case of de novo monoclonal gammopathy of renal significance diagnosed after kidney transplantation and its complexity due to a concomitant chronic active antibody-mediated rejection.

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.

Updates in Plasma Cell Dyscrasias and Related Monoclonal Immunoglobulin-Mediated Renal Disease

Pathogenic roles of monoclonal immunoglobulins in kidney disease have been attributed previously to malignant plasma cell and lymphoproliferative disorders such as multiple myeloma, lymphoplasmacytic lymphoma, chronic lymphocytic leukemia, or amyloid light chain amyloidosis. Improved technology, advancements in molecular diagnostics, and highly sensitive imaging techniques have established the need to redefine monoclonal gammopathies and the kidney disorders that are associated with monoclonal immunoglobulins regardless of tumor burden. This has led to the establishment of monoclonal gammopathy with renal significance (MGRS). MGRS was defined by the International Kidney and Monoclonal Gammopathy Research Group in 2012 as a clonal proliferative disorder that produces a nephrotoxic monoclonal immunoglobulin and does not meet previously defined hematological criteria for treatment of a specific malignancy. MGRS encompasses a wide array of pathologies with knowledge surrounding its incidence, prognosis, and management continuously increasing. This review examines the current evidence on the diagnosis, prognosis, pathogenesis, and therapy of plasma cell dyscrasias and related MGRS.

Proliferative glomerulonephritis with monoclonal IgG deposits: a unique case with a clinical course of over 46 years

BACKGROUND

Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) is a rare entity first described in 2004. We present a case of PGNMID with recurrent hematuria and nephrotic range proteinuria with three biopsies over 46 years.

CASE PRESENTATION

A 79-year-old Caucasian female presents with a history of two separate episodes of biopsy-proven recurrent GN over a course of 46 years. Both biopsies from 1974, and 1987 were reported as membranoproliferative GN (MPGN). The patient presented in 2016 for the third time with symptoms of fluid overload, slight worsening in renal function, and proteinuria along with glomerular hematuria. A third kidney biopsy was performed, and the final diagnosis was proliferative glomerulonephritis with monoclonal IgG/κ deposits.

CONCLUSION

With three renal biopsies obtained over 46 years, our case opens a unique window into the natural history of PGNMID. The three biopsies demonstrate the immunologic and morphologic evolution of PGNMID in the kidney.

Poor outcomes of proliferative glomerulonephritis with monoclonal IgG deposits in renal allografts: a retrospective multicenter study

BACKGROUND

Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) in renal allografts is a rare, renal-limited disease. No study has reported the long-term outcomes and prognostic features of PGNMID in renal allografts in the Chinese population.

METHODS

We retrospectively included transplant patients diagnosed with PGNMID who underwent renal allograft biopsy at three transplant centers from April 2012 to July 2020. We observed the clinicopathologic features, explored the long-term graft survival, and investigated the characteristics associated with the prognosis.

RESULTS

A total of 13 transplant patients with PGNMID were included, out of 3821 biopsies. The mean follow-up time was 55 months since kidney transplantation (KTx). At diagnosis, all patients presented with proteinuria (100%) and most of them with hematuria (92%). IgG3κ (69%) was the main immunofluorescence (IF) subtype. The median graft survival of the total cohort was 17 months from diagnosis and 49 months from kidney transplantation. During follow-up, 9 patients needed dialysis and 2 out of 9 patients who progressed to dialysis died of infection. Primary membranoproliferative glomerulonephritis (MPGN) (P = 0.014) and MPGN pattern at diagnostic biopsy (P < 0.001) were associated with a higher risk of graft loss.

CONCLUSIONS

The long-term outcome of allograft PGNMID was relatively poor in the Chinese population. Primary MPGN and MPGN pattern in renal allograft were associated with  poor outcomes.

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits: an entity associated with distinct diseases and comparison between IgG1 and IgG3 subtypes

OBJECTIVES

The aim of the study was to investigate the clinicopathological characteristics and prognosis of proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) and determine the differences between PGNMID associated with extrarenal disease and without clear etiology as well as the differences between IgG1 and IgG3 subtypes.

METHODS

Data from 46 patients with PGNMID observed from January 2014 to September 2021 in Peking University First Hospital were retrospectively analyzed, including 36 patients without clear etiology (Group A) and 10 patients with extrarenal disease (Group B).

RESULTS

At presentation patients showed proteinuria (95.7%), hematuria (89.1%), renal insufficiency (73.9%), and hypocomplementemia of C3 or C4 (35.6%). Monoclonal immunoglobulin or cell clones were detected in 22.2% of patients (10/45). The monoclonal immunoglobulins deposited in kidney were IgG3 in 40 patients, IgG1 in 5, and IgM in one. Monoclonal IgG1 deposits were more common in Group B than in Group A (4/10 vs. 1/36, p = 0.006). The intensity of glomerular C3 deposition and the frequency of subendothelial deposits in IgG3 subtype were significantly higher than those in IgG1 subtype. During a median follow-up time of 12.2 (range 1-61) months, a higher level of serum creatinine at biopsy and a higher percentage of global glomerulosclerosis were independent predictors of end-stage kidney disease.

CONCLUSIONS

PGNMID associated with extrarenal disease was more likely to have monoclonal IgG1 deposits. PGNMID of IgG3 subtype differs from IgG1 subtype by higher intensity of glomerular C3 deposition and higher frequency of subendothelial deposits. Serum creatinine and global glomerulosclerosis were independent prognostic predictors of ESKD in PGNMID.

[Nephropathy associated with monoclonal immunoglobulins: From clonal expansion B to renal toxicity of pathological immunoglobulins]

Germinal center regulation pathways are often involved in lymphomagenesis and myelomagenesis. Most of the lymphomas (and multiple myeloma) derive from post-germinal center B-cells that have undergone somatic hypermutation and class switch recombination. Hence, B-cell clonal expansion can be responsible for the presence of a monoclonal component (immunoglobulin) of variable titer which, owing to physicochemical properties, can provoke pathologically defined entities of diseases. These diseases can affect any functional part of the kidney, by multiple mechanisms, either well known or not. The presence of renal deposition is influenced by germinal gene involved, immunoglobulin primary structure, post-translational modifications and microenvironmental interactions. The two ways immunoglobulin can cause kidney toxicity are (i) an excess of production (overcoming catabolism power by proximal tubule epithelial cells) with an excess of free light chains within the distal tubules and a subsequent risk of precipitation due to local physicochemical properties; (ii) by structural characteristics that predispose immunoglobulin to a renal disease (whatever their titer). The purpose of this manuscript is to review literature concerning the pathophysiology of renal toxicities of clonal immunoglobulin, from molecular B-cell expansion mechanisms to immunoglobulin renal toxicity.

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.

Treatment with bortezomib for recurrent proliferative glomerulonephritis with monoclonal IgG deposits in kidney allograft. Case report and review of the literature

Proliferative glomerulonephritis with monoclonal immunoglobulin IgG deposits (PGNMID) is an already described form of renal involvement by monoclonal gammopathy. PGNMID is known to recur in kidney allografts. Bortezomib has shown clinical success in the treatment of multiple myeloma. However, its effect for recurrent PGNMID in kidney allografts has rarely been reported. We present the case of a 61-year-old woman who developed recurrent PGNMID 3 weeks after kidney transplantation. This patient was initially treated with steroid pulses (500 mg/day for 2 days) and two cycles of rituximab therapy (200 mg/body). However, disease progression was observed with mesangial matrix expansion and subendothelial deposits by light microscopy and stronger staining for IgG3 and kappa in the mesangial area by Immunofluorescence (IF) microscopy. Thus, we started treatment with bortezomib therapy (1.3 mg/m2, once weekly, on days 1, 8, 15, and 22 in a 5-week cycle, for a total of six cycles). Bortezomib therapy reduced massive proteinuria, although monoclonal immune deposits on IF and the serum creatinine level did not change during the treatment period. Seven months after completion of the first bortezomib course, we decided to prescribe a second course of bortezomib with the same regimen. Each course resulted in a > 50% reduction of proteinuria. Bortezomib may delay the progress of PGNMID in kidney allograft patients.

[Basic nephropathology for pathologists-part 1 : Kidney biopsy-inflammation and immune complexes]

The assessment of kidney biopsies is mainly confined to specialized centres. However, sometimes a kidney biopsy is submitted to a general pathologist, and in addition peritumorous renal parenchyma in tumour nephrectomies can have concomitant non-neoplastic renal disease. Here we present a survey of inflammatory and immunologic changes in all renal compartments, which may in part indicate the need of prompt therapeutic intervention such as in vasculitis, glomerulonephritis and interstitial nephritis. It is important to take into account that renal involvement of vasculitis is mainly centred in glomeruli and only to a much lesser extent in arteries, and that the frequently observed interstitial inflammation very often is an epiphenomenon of another primary kidney disease and not an independent disease process. Typical renal patterns of injury are emphasised.

Glomerulonephritis with non-Randall-type, non-cryoglobulinemic monoclonal immunoglobulin G deposits [PGNMID and ITG]

Background

Glomerulonephritis (GN) with non-Randall-type, non-cryoglobulinemic monoclonal immunoglobulin G deposits encompasses rare diseases [proliferative GN with non-organized deposits (PGNMID) and immunotactoid GN] that cannot be distinguished without ultrastructural analysis by electron microscopy (EM).

Methods

Here, we report and analyze the prognosis of 41 EM-proven (PGNMID for 39/41) and 22 non-EM-proven/DNAJB9-negative cases, diagnosed between 2001 and 2019 in 12 French nephrology centers.

Results

Median serum creatinine (SCr) at presentation was 150 [92-256] μmol/L. The predominant histological pattern was membranoproliferative GN (79%), with IgG3 (74%) kappa (78%) deposits the most frequently observed. Disease presentation and patient management were similar between EM-proven and non-EM-proven cases. A serum monoclonal spike was detected for 21 patients and 10 had an underlying hematological malignancy. First-line therapy was mixed between clone-targeted therapy (n = 33), corticosteroids (n = 9), and RAAS-inhibitors (n = 19). After six months, nine patients achieved complete and 23 partial renal recovery. In univariate analysis, renal recovery was associated with baseline SCr (OR 0.70, p = 0.07). After a median follow-up of 52 [35–74] months, 38% of patients had progressed to end-stage kidney disease independently associated with baseline SCr (HR 1.41, p = 0.003) and glomerular crescentic proliferation (HR 4.38, p = 0.004).

Conclusions

Our results confirm that non-cryoglobulinemic and non-Randall GN with monoclonal IgG deposits are rarely associated with hematological malignancy. The prognosis is uncertain but may be improved by early introduction of a specific therapy.

Monoclonal Gammopathy-Related Kidney Diseases

Monoclonal gammopathies occur secondary to a broad range of clonal B lymphocyte or plasma cell disorders, producing either whole or truncated monoclonal immunoglobulins. The kidneys are often affected by these monoclonal proteins, and, although not mutually exclusive, can involve the glomeruli, tubules, interstitium, and vasculature. The nephrotoxic potential of these monoclonal proteins is dependent on a variety of physicochemical characteristics that are responsible for the diverse clinicopathologic manifestations, including glomerular diseases with organized deposits, glomerular diseases with granular deposits, and other lesions, such as C3 glomerulopathy and thrombotic microangiopathy with unique pathophysiologic features. The diseases that involve primarily the tubulointerstitial and vascular compartments are light chain cast nephropathy, light chain proximal tubulopathy, crystal-storing histiocytosis, and crystalglobulin-induced nephropathy with distinct acute and chronic clinicopathologic features. The diagnosis of a monoclonal gammopathy-related kidney disease is established by identification of an underlying active or more commonly, low-grade hematologic malignancy, serologic evidence of a monoclonal gammopathy when detectable, and most importantly, monoclonal protein-induced pathologic lesions seen in a kidney biopsy, confirming the association with the monoclonal protein. Establishing a diagnosis may be challenging at times, particularly in the absence of an overt hematologic malignancy, with or without monoclonal gammopathy, such as proliferative glomerulonephritis with monoclonal immunoglobulin deposits. Overall, the treatment is directed against the underlying hematologic disorder and the potential source of the monoclonal protein.

An update of proliferative glomerulonephritis with monoclonal immunoglobulin deposits

As aging increases, monoclonal gammopathy is becoming more common, and monoclonal gammopathy of renal significance (MGRS) is gaining attention due to frequent renal involvement. Among MGRS, proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) is a special category. The disease was first described in 2004, and the research history on it is relatively short. Compared with other MGRS, the detection rate of circulating clones is lower in patients with PGNMID, which is easy to be missed and misdiagnosed in clinical work. In this review, the etiology and clinical features of PGNMID are discussed. It is noted that PGNMID is not only associated with MGRS, but also with malignancy, infection, and other factors. PGNMID is not a disease exclusive to the elderly, young people can also develop this disease. Due to the low detection rate of circulating clones in most patients, confirmation of the disease needs to be combined with renal pathology, which emphasizes the importance of completing light and heavy chain subtype staining. Treatment options for patients with PGNMID differ by etiology. For MGRS-associated PGNMID, the current treatment is primarily empirical and more research evidence is needed to fill the treatment gap.

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.

Heavy and light chains all at once: A new immunofluorescence technique to evaluate monoclonal immunoglobulin deposits

Tools to identify monoclonal Ig deposits within tissue specimens include immunofluorescence (IF) staining on frozen tissue for Ig heavy chains and light chains, pronase IF to unmask monoclonal Ig deposits not seen by IF staining on frozen tissue, and IF staining for IgG subclasses (IgG1-IgG4). In this issue of Kidney International, a novel diagnostic tool is introduced: IF staining for conformational epitopes at the junction of the Ig heavy chains and light chains. This technique has the potential to significantly enhance our ability to evaluate apparent monoclonal forms of renal disease.

The Clone Wars: Diagnosing and Treating Dysproteinemic Kidney Disease in the Modern Era

Dysproteinemic kidney diseases are disorders that occur as the result of lymphoproliferative (B cell or plasma cell) disorders that cause kidney damage via production of nephrotoxic monoclonal immunoglobulins or their components. These monoclonal immunoglobulins have individual physiochemical characteristics that confer specific nephrotoxic properties. There has been increased recognition and revised characterization of these disorders in the last decade, and in some cases, there have been substantial advances in disease understanding and treatments, which has translated to improved patient outcomes. These disorders still present challenges to nephrologists and patients, since they are rare, and the field of hematology is rapidly changing with the introduction of novel testing and treatment strategies. In this review, we will discuss the clinical presentation, kidney biopsy features, hematologic characteristics and treatment of dysproteinemic kidney diseases.

Immunotactoid glomerulopathy is a rare entity with monoclonal and polyclonal variants

Immunotactoid glomerulopathy (ITG) is a rare form of glomerulonephritis for which our understanding is limited to case reports and small case series. Herein we describe the clinical, pathologic, and outcome characteristics of 73 patients with ITG who typically presented with proteinuria, hematuria, and renal insufficiency. Hematologic disorders were present in 66% of patients, including lymphoma in 41% (mainly chronic lymphocytic leukemia/small lymphocytic lymphoma), monoclonal gammopathy in 20%, and multiple myeloma in 6%. Light microscopy revealed endocapillary proliferative (35%), membranoproliferative (29%) and membranous (29%) patterns of glomerular involvement. Electron microscopy revealed characteristic microtubular deposits with a diameter of 14-60 nm, hollow cores, frequent parallel alignment, and a predominant distribution outside of the lamina densa of the glomerular basement membrane. Importantly, immunofluorescence revealed IgG-dominant staining which was light chain and IgG subclass restricted in 67% of cases, indicating monoclonal composition. This finding was used to distinguish monoclonal and polyclonal variants of ITG. As compared to polyclonal, monoclonal ITG had a higher incidence of lymphoma (53% vs. 11%), multiple myeloma (8% vs. 0), and monoclonal gammopathy (22% vs. 16%). Monoclonal ITG was more commonly treated with clone-directed therapy, which was associated with more frequent remission and less frequent end stage kidney disease. Thus, a third of ITG cases are polyclonal but a quarter of these cases are associated with hematologic conditions, underscoring the need for hematologic evaluation in all patients with ITG. Hence, based on these distinctions, ITG should be subclassified into monoclonal and polyclonal variants. Prognosis of ITG is good if the underlying hematologic condition is treated.