Membranous nephropathy with masked polyclonal IgG deposits associated with primary Sjögren's syndrome

A case of lupus nephritis with masked polyclonal IgG presenting as severe AKI, successfully treated and withdrawn from hemodialysis: a case report

Lupus nephritis (LN) is well-known as an immune-mediated glomerulonephritis characterized by the full-house pattern of immunoglobulin (Ig) and complement deposition. The "masked IgG" is a recently recognized concept in which IgG appears negative on standard frozen sections but becomes positive on formalin-fixed paraffin-embedded (FFPE) tissue sections treated with pronase. Typically, monoclonal IgGκ deposition is observed in such cases. We report a unique case of LN in a 69-year-old male with urinary abnormalities and renal dysfunction. Kidney biopsy revealed necrotizing glomerulonephritis and crescent formation with massive subepithelial and mild subendothelial electron-dense deposits, consistent with Class III(A/C) + V LN. However, immunofluorescence using a frozen sample showed pauci-immune features. In contrast, FFPE with pronase digestion showed strong positive for IgG and light chain-kappa and lambda indicating "masked polyclonal IgG". The patient developed AKI, which progressed to ESRD, necessitating the initiation of hemodialysis. Notably, 5 months after the initiation of treatment with steroids and mycophenolate mofetil, the patient experienced an improvement in renal function and ultimately achieved withdrawal from hemodialysis. A repeat kidney biopsy revealed progression to Class IV(A/C) + V lupus nephritis and Ig and complements were detected in normal immunofluorescence using a frozen sample. Further, mass spectrometry analysis of glomeruli in both biopsies identified a "high-temperature requirement A serine peptidase 1", HTRA1. In conclusion, this was a pathologically extremely rare case of lupus nephritis (LN) with masked polyclonal IgG, in which HTRA1 was detected in the kidney biopsy.

Diagnostic Immunostaining of Renal Biopsies: An Overview of Markers for Glomerular Diseases

Background

The analysis of a renal biopsy is made complex by multifactorial etiologies involving different renal compartments. Recent proteomic data, pattern-based classification, and a better understanding of various glomerular renal diseases have underscored the importance of immunohistology as an integral part of the diagnostic evaluation of renal biopsies. These include immunofluorescence on formalin-fixed paraffin-embedded renal tissue (IF-P), IgG subclass staining, typing of amyloid, and other organized deposits, classification of membranous nephropathy, etc.

Summary

We describe the recent immunohistological markers on immunofluorescence (IF) and immunohistochemistry (IHC) on fresh and formalin-fixed paraffin-embedded renal native biopsies for proper evaluation and classification of glomerular diseases. The article also provides information on the diagnostic utility, interpretation, and established antibody clones described in the literature for various glomerular diseases. The indications of IF-P in renal biopsies are also outlined.

Key Messages

Immunohistology has become integral to diagnosing and classifying various glomerular renal diseases. A specific protein or antigen-based classification has prognostic and therapeutic implications. Additionally, it provides clue for screening the patient for an underlying etiology.

Establishing a differential diagnosis model between primary membranous nephropathy and non-primary membranous nephropathy by machine learning algorithms

CONTEXT

Four algorithms with relatively balanced complexity and accuracy in deep learning classification algorithm were selected for differential diagnosis of primary membranous nephropathy (PMN).

OBJECTIVE

This study explored the most suitable classification algorithm for PMN identification, and to provide data reference for PMN diagnosis research.

METHODS

A total of 500 patients were referred to Luo-he Central Hospital from 2019 to 2021. All patients were diagnosed with primary glomerular disease confirmed by renal biopsy, contained 322 cases of PMN, the 178 cases of non-PMN. Using the decision tree, random forest, support vector machine, and extreme gradient boosting (Xgboost) to establish a differential diagnosis model for PMN and non-PMN. Based on the true positive rate, true negative rate, false-positive rate, false-negative rate, accuracy, feature work area under the curve (AUC) of subjects, the best performance of the model was chosen.

RESULTS

The efficiency of the Xgboost model based on the above evaluation indicators was the highest, which the diagnosis of PMN of the sensitivity and specificity, respectively 92% and 96%.

CONCLUSIONS

The differential diagnosis model for PMN was established successfully and the efficiency performance of the Xgboost model was the best. It could be used for the clinical diagnosis of PMN.

Chasing the Zebra: a case of membranous-like Glomerulopathy with SSA/RO52 deposits and no overt connective tissue disease

BACKGROUND

The nature of the deposits in immune-mediated glomerulonephritis with a membranous pattern and masked IgG-Kappa deposits (MGMID) remains still to be elucidated.

CASE PRESENTATION

We present a case of 33-year-old woman developing a continuous asymptomatic proteinuria (0.8-1 g/24 h) with no overt connective tissue diseases. She tested positive at high titers for SSA antibodies (Ro52 838 UI/mL, Ro60 2716 UI/mL) and at the kidney biopsy histological findings were compatible with an immune-mediated glomerulonephritis with a membranous pattern and masked IgG-Kappa deposits. Also, we demonstrated a positive immunohistochemistry staining for anti-Ro52-SSA antibodies, with a granular positivity in mesangium and along rare glomerular capillaries. To date, only one case of a patient with overt diagnosis of Sjögren's syndrome with MGMID has been described but a pathogenic role for SSA and SSB antibodies has never been proven.

CONCLUSIONS

In this case, we described for the first time by immunohistochemistry a Ro52+ granular positivity in the mesangium and glomerular capillaries, potentially paving the way for a better understanding of MGMID.

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

We report a case of membranous nephropathy with monoclonal immunoglobulin (Ig)M lambda deposits in a patient with IgM monoclonal gammopathy, in whom histological changes were observed on repeat renal biopsy. A 72-year-old Japanese woman was referred to our hospital because of massive proteinuria. A prominent increase in monoclonal IgM lambda level was identified, and she was diagnosed as having IgM monoclonal gammopathy of undetermined significance. Renal biopsy showed glomerular subepithelial electron-dense deposits that were found to be granular deposits of IgM lambda but not kappa or IgG by immunofluorescence staining, resulting in a diagnosis of membranous nephropathy with monoclonal IgM deposits. The second biopsy, which was performed 2 years later because of exacerbation of her nephrotic syndrome, demonstrated less immunofluorescence staining of IgM, and dominant IgG2 deposition without light chain restriction. Interestingly, immunostaining for thrombospondin-type-1-domain-containing-7A was positive in both renal biopsy tissues, although the second biopsy showed clearly stronger immunoreactivity. The effect of steroid therapy was limited; however, rituximab treatment improved both the hematological and renal abnormalities. Solitary deposition of IgM in membranous nephropathy is a quite rare condition. To our knowledge, this is the first case of monoclonal gammopathy of renal significance presenting as membranous nephropathy with monoclonal IgM deposits, in which chronological immunohistochemical changes were observed and rituximab therapy was effective.