Monoclonal gammopathy of undetermined significance: an update for nephrologists

Congophilic fibrils in the glomeruli with polyclonal immunoglobulin gamma staining - another cause for diagnostic overlap: A case report

BACKGROUND

Glomerulopathy with fibrillary deposits is not uncommon in routine nephropathology practice, with amyloidosis and fibrillary glomerulonephritis being the two most frequently encountered entities. Renal amyloid heavy and light chain (AHL) is relatively uncommon and its biopsy diagnosis is usually limited to cases that show strong equivalent staining for a single immunoglobulin (Ig) heavy chain and a single light chain, further supported by mass spectrometry (MS) and serum studies for monoclonal protein. But polyclonal light chain staining can pose a challenge.

CASE SUMMARY

Herein we present a challenging case of renal AHL with polyclonal and polytypic Ig gamma (IgG) staining pattern by immunofluorescence. The patient is a 62-year-old Caucasian male who presented to an outside institution with a serum creatinine of up to 8.1 mg/dL and nephrotic range proteinuria. Despite the finding of a polyclonal and polytypic staining pattern on immunofluorescence, ultrastructural study of the renal biopsy demonstrated the presence of fibrils with a mean diameter of 10 nm. Congo red was positive while DNAJB9 was negative. MS suggested a diagnosis of amyloid AHL type with IgG and lambda, but kappa light chains were also present supporting the immunofluorescence staining results. Serum immunofixation studies demonstrated IgG lambda monoclonal spike. The patient was started on chemotherapy. The chronic renal injury however was quite advanced and he ended up needing dialysis shortly after.

CONCLUSION

Tissue diagnosis of AHL amyloid can be tricky. Thorough confirmation using other available diagnostic techniques is recommended in such cases.

Monoclonal Gammopathy of Undetermined Significance: A Comprehensive Review

Monoclonal Gammopathy of Undetermined Significance (MGUS) is an asymptomatic premalignant plasma cell dyscrasia with a predominate rise of the IgG immunoglobulin fraction without end-organ damage, often diagnosed incidentally. Despite its progression into various subsequent forms of hematological malignancies, MGUS remains underdiagnosed. A literature search was conducted using the Medline, Cochrane, Embase, and Google Scholar databases, including articles published until December 2022. Keywords used encompassed "Monoclonal Gammopathy of Undetermined Significance," "Plasma Cell dyscrasia," "Monoclonal gammopathy of renal significance," and "IgM Monoclonal gammopathy of Undetermined Significance," This study aimed to conduct a critical review to update knowledge regarding the pathophysiology, risk factors, clinical features, diagnostic protocols, complications, and current and novel treatments for MGUS. We recommend a multidisciplinary approach to manage MGUS due to the complexity of the illness's etiology, diagnosis, and therapy. This comprehensive review also highlights future prospects, such as developing screening protocols for at-risk populations, prevention of disease progression by early diagnosis through genome-wide association studies, and management using Daratumumab and NSAIDs.

Santos M, Esteves J. Monoclonal Gammopathy of Renal Significance and Thrombotic Microangiopathy: A Case Report

Monoclonal gammopathy of renal significance (MGRS) is a group of pathologies that includes all kidney disorders related to a monoclonal protein in patients without diagnostic criteria for B-cell malignancies. There are multiple MGRS-associated kidney disorders, and more are still being discovered, which makes this diagnosis challenging. The relationship between monoclonal gammopathies and thrombotic microangiopathy (TMA) is of growing interest in literature. This article describes the case of a patient with newly diagnosed MGRS, presenting with rapidly progressing kidney failure and with histologic characteristics of TMA. The patient progressed to end-stage renal disease (ESRD) despite treatment with plasmapheresis and clone-directed therapy, as is currently advised in the literature. Although rare, the association between these two entities should not be unnoticed because of patients' renal and vital prognosis.

Rate and Predictors of Finding Monoclonal Gammopathy of Renal Significance (MGRS) Lesions on Kidney Biopsy in Patients with Monoclonal Gammopathy

BACKGROUND

Little is known about the rate and predictors of finding lesions of monoclonal gammopathy (MG) of renal significance (MGRS) on kidney biopsy specimens among patients with MG.

METHODS

We reviewed the medical records from 2013 to 2018 at the Mayo Clinic in Rochester, Minnesota, to identify patients with MG and whether they had undergone a kidney biopsy. In a more select group of patients with MG from 2017 to 2018, we conducted a review of records to determine how many had underlying CKD, which of those with CKD had undergone a kidney biopsy, and reasons for deferring a kidney biopsy.

RESULTS

Between 2013 and 2018, we identified 6300 patients who had MG, 160 (2.5%) of whom had undergone a kidney biopsy. Of the 160 patients, 64 (40%) had an MGRS lesion; amyloid light chain amyloidosis, the most common finding, accounted for nearly half of these lesions. In the non-MGRS group comprising 96 patients, 23 had arteriosclerosis, the most common finding. In multivariate analysis, strong predictors of finding an MGRS lesion included the presence of an elevated free light chain ratio, proteinuria, and hematuria. Among 596 patients with CKD and MG from 2017 to 2018, 62 (10.4%) underwent a kidney biopsy. Kidney biopsy was deferred for 70 patients (20%); for 62 of the 70, the diagnosis was already known, and eight were not candidates for therapy. Younger age and higher proteinuria and serum creatinine levels increased the likelihood that the patient would undergo a kidney biopsy.

CONCLUSIONS

Proteinuria ≥1.5 g/d, hematuria, and an elevated free light chain ratio increase the likelihood of finding MGRS, and a kidney biopsy should be highly considered in such patients.

Modern approaches to the detection of monoclonal gammopathy of undetermined significance (MGUS) in patients with kidney diseases

Monoclonal gammopathy (MG) is not only the state preceding of hematological neoplasms, but also associated with non - hematological diseases, in particular kidney damage. Aim. To assess the diagnostic value of “Freelite” methods in addition to electrophoresis (EF) and immunofixation (IF) of serum and urine proteins for detecting MG in patients with kidney diseases. Materials and methods. 87 patients with kidney damage, in which MG was established using the method of electrophoresis of serum proteins (EF), immunofixation (IF) and the method of free light chains determination - FLC “Freelite” were selected. The diagnostic value of three - component serum panel was compared with EF and IF. Results and discussion. AL-amyloidosis with kidney involvement was diagnosed in 41% patients, cryoglobulinemic glomerulonephritis (cryo GN) - in 18%, chronic glomerulonephritis (CGN) - in 35%, also there was small number of patients with light chain disease and cast - nephropathy. Determination of MG using EP was possible only in 38 (44%). Adding to the serum electrophoretic methods instead of the “Freelite” method, the urine EF and IF reduced the number of missed patients with monoclonal gammopathy from 24 (27%) to 11 (13%), including in the subgroup of patients with AL-amyloidosis but did not reach the sensitivity of the three - component serum screening panel. In 10 (11.5%) MG was represented only by intact mIg with one type of light chain, either κ or λ. Most often - in 25% of patients, intact monoclonal gammopathy was observed in HCV (+) cryo GN. A combination of intact mIgM, mIgG or mIgA with mFLC, was detected in 37 (42.5%). In almost half (46%) of the patients, only mFLC was detected - an abnormal κ/λ ratio. Conclusion: The serum screening panel EF + IF + “Freelite” spreads the low - grade monoclonal gammopathy recognition (MGUS) and should be included in the algorithm of examining patients with kidney disease.

Renal lesions associated with monoclonal gammopathies of undetermined significance: clinical forms, mechanisms of development, approaches to treatment

The term «monoclonal gammopathies of undetermined significance» (MGUS) was introduced by R. Kyle in 1978 to designate the condition characterized by the presence ofsmall amounts ofM-protein in the serum. In some patients, such condition remains benign for a long time but predetermines for the development of multiple myeloma and other B-lymphocytic tumours. Also, it can provoke non-cancerous diseases due to the toxic action of monoclonal proteins (immunoglobulins and free light chains) on various organs, especially kidneys. MGUS-associated renal lesions include glomerulopathies with organized deposits, such as AL-amyloidosis (amyloid light chain of immunoglobulin), cryoglobulinic and immunotactoid glomerulonephritis, and with unorganized deposits (light chain deposition and proliferative forms of idiopathic glomerulonephritis. The available experimental data throw light on the possible mechanisms of renal lesions. We summarized the literature data and original observations to describe methods for differential diagnostics of MGUS-associated renal lesions including the highly sensitive test for free light chine identification (Freelite method) and principles of pathogenetic treatment by the impact on the pathological B-cell clone.

[Oligosecretory monoclonal gammopathy with renal involvement]

The article deals with the so-called monoclonal gammopathy of undetermined significance (MGUS), which is being actively explored in the world and has been recently investigated in Russia. It indicates the principles of identifying the phenotypes of MGUS and criteria for assessing the risk of its progression to cancer. There is an update on the possible involvement of monoclonal proteins in the pathogenesis of certain non-neoplastic kidney diseases, renal injuries in particular. The paper gives their classification and enumerates differential diagnostic techniques, including the Freelite method, a highly sensitive one to determine free light chains (FLC), prognostic criteria, and approaches to treating each separate form in relation to the phenotype of a monoclonal protein. The authors present their own data on detection rates for MGUS at a multidisciplinary hospital and a clinical case of MGUS-associated membranoproliferative glomerulonephritis, by justifying a treatment regimen containing bortezomib (velcade).

Progression of Monoclonal Gammopathy with Undetermined Significance to Multiple Myeloma Diagnosed by Kidney Biopsy: A Case Report

Monoclonal gammopathy with undetermined significance (MGUS) carries a risk of progression to multiple myeloma, and progression is usually diagnosed with changes in M-protein or bone marrow biopsy. We report a case of 62-year-old female patient showing MGUS progression to multiple myeloma without significant changes in M-protein but diagnosed by kidney biopsy. During the follow-ups, azotemia and tubular proteinuria were aggravated without elevation of M-protein. Kidney biopsy showed intratubular and glomerular inclusions associated with plasma cell dysplasia. The progression of MGUS to multiple myeloma was diagnosed by this kidney biopsy. The patient's renal function and tubular proteinuria were markedly improved after chemotherapy.

Serum cystatin C and serum and urine NGAL in the kidney function assessment of patients with MGUS

OBJECTIVES

Monoclonal gammopathy of undetermined significance (MGUS) occurs without other symptoms, although monoclonal proteins can cause kidney injuries. Here, we assessed kidney function and identified the best follow-up parameters in patients with MGUS without kidney damage symptoms.

METHODOLOGY

Forty-six patients with MGUS were included in the study group. The control group (CRT, n = 23) consisted of healthy subjects matched for age and sex. Serum cystatin C was determined using an immunonephelometric method, serum and urine neutrophil gelatinase-associated lipocalin (NGAL) was measured with an immunoenzymatic method, and cathepsin B activity was determined fluorometrically.

RESULTS

Serum cystatin C and urine NGAL were higher, and serum NGAL was lower in MGUS patients compared with CRT. Neither serum cystatin C, nor serum or urine NGAL, correlated with the biomarkers of MGUS. The serum activity of cathepsin B did not differ between groups and did not correlate with serum cystatin C. Serum cystatin C correlated with serum creatinine, while serum NGAL did not correlate with serum creatinine or cystatin C. The estimated glomerular filtration rates (eGFRs) in MGUS were within normal range and correlated with serum cystatin C. The strongest correlation was observed for CKD-EPI. Seven patients presented with albuminuria >30 mg/day. There was a correlation between albuminuria in this group and λ free light chains.

CONCLUSIONS

The kidney function in MGUS patients is impaired, although there are no clinical and standard laboratory test manifestations. Cystatin C and urine, but not serum, NGAL should be considered markers for kidney injury. CKD-EPI is recommended for eGFR assessment.

Differential diagnosis of glomerular disease: a systematic and inclusive approach

BACKGROUND

Glomerular disease is a complex and evolving topic. In evaluating a specific case it is not unusual for the clinician to ask: 'Am I missing something? Should I biopsy? When? Should I treat first, then biopsy?' This work, which is both evidence and experience based, is intended to address each of these concerns and many other issues relevant to the differential diagnosis of glomerular disease.

SUMMARY

The central approach is the use of diagnostic algorithms that are based on quantitative measures routinely obtained early in the course of the diagnostic evaluation. The algorithms are designed to be easy to navigate, systematic, and inclusive. Also provided is a detailed and prioritized list of recommended diagnostic testing, and the rationale for each test.

KEY MESSAGE

This work is intended to facilitate accurate diagnosis in the individual patient presenting with evidence of glomerular disease.