Standardized reporting of monoclonal immunoglobulin-associated renal diseases: recommendations from a Mayo Clinic/Renal Pathology Society Working Group

KDOQI US Commentary on the 2021 KDIGO Clinical Practice Guideline for the Management of Glomerular Diseases

The KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases represents the first update to this set of recommendations since the initial set of KDIGO guideline recommendations was published in 2012. The pace of growth in our molecular understanding of glomerular disease has quickened and a number of newer immunosuppressive and targeted therapies have been introduced since the original set of guideline recommendations, making such an update necessary. Despite these updates, many areas of controversy remain. In addition, further updates since the publication of KDIGO 2021 have occurred which this guideline does not encompass. With this commentary, the KDOQI work group has generated a chapter-by-chapter companion opinion article that provides commentary specific to the implementation of the KDIGO 2021 guideline in the United States.

Acute glomerulonephritis

Glomerulonephritis is a heterogeneous group of disorders that present with a combination of haematuria, proteinuria, hypertension, and reduction in kidney function to a variable degree. Acute presentation with full blown nephritic syndrome or rapidly progressive glomerulonephritis is uncommon and is mainly restricted to patients with post-infectious glomerulonephritis, anti-neutrophil cytoplasmic antibodies-associated vasculitis, and anti-glomerular basement membrane disease. Most frequently, patients present with asymptomatic haematuria and proteinuria with or without reduced kidney function. All glomerulonephritis disorders can show periods of exacerbation, but disease flairs characteristically occur in patients with IgA nephropathy or C3 glomerulopathy. The gold standard for the diagnosis of a glomerulonephritis is a kidney biopsy, with a hallmark glomerular inflammation that translates into various histopathological patterns depending on the location and severity of the glomerular injury. Traditionally, glomerulonephritis was classified on the basis of the different histopathological patterns of injury. In the last few years, substantial progress has been made in unravelling the underlying causes and pathogenetic mechanisms of glomerulonephritis and a causal approach to the classification of glomerulonephritis is now favoured over a pattern-based approach. As such, glomerulonephritis can be broadly classified as immune-complex glomerulonephritis (including infection-related glomerulonephritis, IgA nephropathy, lupus nephritis, and cryoglobulinaemic glomerulonephritis), anti-neutrophil cytoplasmic antibodies-associated (pauci-immune) glomerulonephritis, anti-glomerular basement membrane glomerulonephritis, C3 glomerulopathy, and monoclonal immunoglobulin-associated glomerulonephritis. We provide an overview of the clinical presentation, pathology, and the current therapeutic approach of the main representative disorders in the spectrum of glomerulonephritis.

Towards harmony in defining and reporting glomerular diseases on kidney biopsy

PURPOSE OF REVIEW

To review recent efforts to develop uniformity and precision in defining individual glomerular histologic and ultrastructural lesions and proposals for developing greater uniformity in reporting of glomerular diseases.

RECENT FINDINGS

Over the past 2 decades, scoring systems for multiple glomerular diseases have emerged, as have several consortia for the study of glomerular diseases. However, one important limitation faced by renal pathologists and nephrologists has been a lack of uniformity and precision in defining the morphologic lesions seen by light and electron microscopy on which the scoring systems are based. In response to this, the Renal Pathology Society organized a working group that over 4 years arrived at consensus definitions for many such lesions. These definitions can be applied within the context of scoring systems for different glomerular diseases, and recently proposed reporting systems based on pathogenic categories and for defining the overall severity of chronic changes.

SUMMARY

From extensive discussions a panel of 13 renal pathologists reached consensus in defining 47 individual glomerular lesions seen on light microscopy and 56 glomerular lesions and key normal structures seen by electron microscopy. Validation of the impact of these consensus definitions on interobserver agreement in lesion identification is currently underway.

Pregnancy-associated proliferative glomerulonephritis with monoclonal immunoglobulin deposits

We report a young woman presented with nephrotic syndrome and normotension during every pregnancy and achieved complete remissions after the deliveries. We thus inferred that her nephrotic syndrome was closely associated with pregnancy. Kidney biopsies were perfromed and showed different histologic patterns: the first biopsy showed a pattern of endocapillary proliferative glomerulonephritis; the second biopsy revealed proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) with features of membranous nephropathy. With regard to presentation during the second trimester of pregnancy, achieving complete remission after delivery, and no relapse during the follow-up period, pregnancy associated PGNMID is suggested. To our best knowledge, this is the first reported case of PGNMID associated with pregnancy.

Diagnosis of amyloid beyond Congo red

PURPOSE OF REVIEW

Amyloidoses are a group of rare and heterogeneous diseases in which abnormally folded proteins deposit in tissues and lead to organ damage. A brief review of advances in the diagnosis of extracerebral systemic amyloidoses in the context of recent advances in their clinical management is provided.

RECENT FINDINGS

Although steady progress in the treatment of AL and AA has evolved over many years, significant advances in the treatment of ATTR, transthyretin-derived amyloidosis, have been achieved only recently. This coincides with the emergence of nontissue diagnosis of cardiac ATTR in both the hereditary and wild-type settings. The latter is emerging as possibly the most prevalent type of systemic amyloidosis.Available treatments are amyloid protein type dependent and, hence, following amyloid detection, amyloid protein typing is necessary. Although mass spectrometry has emerged as the preferred method of amyloid typing, careful application of immune methods is still clinically useful but caution and experience, as well as awareness of the limitations of each method, are necessary in their interpretation.

SUMMARY

Despite significant advances in the treatment of the systemic amyloidoses, outcomes remain poor, primarily due to delays in diagnosis. Precise diagnosis of the amyloid protein type is critical for treatment selection.