Mechanisms of light chain injury along the tubular nephron

Immunoglobulin repertoire sequencing and de novo sequencing - Powerful tools for identifying free light chains from patients with light chain cast nephropathy

In patients with light chain cast nephropathy (LCCN), abundantly produced monoclonal immunoglobulin free light chains (FLCs) play a vital role in pathogenesis. Determining the precise sequences of patient-derived FLCs is therefore highly desirable. Although immunoglobulin repertoire sequencing (5' RACE-seq) has been proven to be sensitive enough to provide full-length V(D)J region (variable, diversity and joining genes) of FLCs using bone marrow samples, an invasive and bone marrow independent method is still in demand. Here a de novo sequencing workflow based on the bottom-up proteomics for patient-derived FLCs was established. PEAKS software was used for the de novo sequencing of peptides that were further assembled into full-length FLC sequences. This de novo protein sequencing method can obtain the full-length amino acid sequences of FLCs, and had been shown to be as reliable as 5' RACE-seq. The two LCCN sequences derived from above the two methods were identical, and they possessed more hydrophobic or nonpolar amino acids compared with the corresponding germline, which may be associated with the pathogenesis.

Concurrent Crystalline Light-Chain Proximal Tubulopathy and Membranous Nephropathy: A Case Report and Literature Review

Light-chain proximal tubulopathy (LCPT) is typically characterized by the intracytoplasmic deposition of light chains within the proximal tubular epithelial cells, which is usually classified into crystalline and noncrystalline subgroups. Membranous nephropathy (MN) is a common glomerular disease characterized by diffused subepithelial electron-dense deposits along the capillary loop accompanied by the effacement and microvillus transformation of the foot process. Here, we report a biopsy-confirmed case of a concurrence of LCPT with crystals (κ light chains restricted) and antigen-undetermined MN in a male patient. The patient presented with low-molecular-weight proteinuria, increased serum creatinine levels, and incomplete Fanconi syndrome. To our knowledge, this is the first report of a concurrence of LCPT and independent MN of unknown target antigens, which may enrich our recognition of monoclonal gammopathy of renal significance with synchronous MN.

Combined crystal-storing histiocytosis, light chain proximal tubulopathy, and light chain crystalline podocytopathy in a patient with multiple myeloma: a case report and literature review

BACKGROUND

Crystal-storing histiocytosis (CSH), light chain proximal tubulopathy (LCPT), and light chain crystalline podocytopathy (LCCP) are rare complications of multiple myeloma (MM) or monoclonal gammopathy of renal significance, and their diagnoses are challenging.

CASE PRESENTATION

In this case, a 69-year-old Chinese woman presented with suspicious Fanconi syndrome with renal insufficiency. Immunofixation electrophoresis of both serum and urine revealed elevated immunoglobulin G kappa (IgGkappa) and kappa light chain. Bone marrow aspirate revealed 15% plasma cells with considerable cytoplasmic granular inclusions and needle-shaped crystals. Renal biopsy confirmed the final pathologic diagnosis of kappa-restricted CSH, combined LCPT and LCCP by immunoelectron microscopy. A number of special casts were present which could easily be misdiagnosed as light chain cast nephropathy. Immunofluorescence on frozen tissue presented false negative for kappa light chain, as ultimately proven by paraffin-embedded tissue after pronase digestion. MM and CSH were diagnosed, and two cycles of chemotherapy were given. The patient subsequently refused further chemotherapy, and her renal function remained relatively stable during a 2.5-year follow-up period.

CONCLUSIONS

In conclusion, we report a rare case of generalized kappa-restricted CSH involving bone marrow and kidney, combined with LCPT and LCCP, provide a comprehensive summary of renal CSH, and propose a new nomenclature of monoclonal immunoglobulin-induced crystalline nephrology. The presentation of monoclonal immunoglobulin and Fanconi syndrome should suggest the presence of monoclonal immunoglobulin-induced crystalline nephrology. Use of paraffin-embedded tissue after pronase digestion and immunoelectron microscopy is beneficial to improve the sensitivity of diagnosis.

Hypophosphatemia in Patients With Multiple Myeloma

Hypophosphatemia is among the most common electrolyte abnormalities, especially among patients with underlying malignancies, and is frequently associated with adverse prognoses. Phosphorus levels are regulated through a number of mechanisms, including parathyroid hormone (PTH), fibroblast growth factor-23 (FGF-23), vitamin D, and other electrolyte levels themselves. Clinically, the findings are nonspecific, and the diagnosis is frequently delayed. This article is a narrative literature review. The PubMed database was searched for relevant articles pertaining to hypophosphatemia causes and consequences in patients suffering from multiple myeloma. We found a variety of causes of hypophosphatemia in patients with multiple myeloma. Tumor-induced osteopenia, although more common among patients with small squamous cell carcinomas, can occur with multiple myeloma as well. Additionally, both light chains themselves and medications can trigger Fanconi syndrome, which leads to phosphorus wasting by the kidney. Bisphosphonates, in addition to being a possible cause of Fanconi syndrome, lead to a decrease in calcium levels, which then stimulates parathyroid hormone (PTH) release, predisposing the patient to significant hypophosphatemia. Additionally, many of the more modern medications used to manage multiple myeloma have been associated with hypophosphatemia. A better understanding of those mechanisms may give clinicians a clearer idea of which patients may need more frequent screening as well as what the potential triggers in the individual patient may be.

Multiple myeloma with acute light chain cast nephropathy

Light chain cast nephropathy (LCCN) is a leading cause of acute kidney injury (AKI) in patients with multiple myeloma (MM) and is now defined as a myeloma defining event. While the long-term prognosis has improved with novel agents, short-term mortality remains significantly higher in patients with LCCN especially if the renal failure is not reversed. Recovery of renal function requires a rapid and significant reduction of the involved serum free light chain. Therefore, proper treatment of these patients is of the utmost importance. In this paper, we provide an algorithm for treatment of MM patients who present with biopsy-proven LCCN or in those where other causes of AKI have been ruled out. The algorithm is based on data from randomized trial whenever possible. When trial data is not available, our recommendations is based on non-randomized data and expert opinions on best practices. We recommend that all patients should enroll in a clinical trial if available prior to resorting to the treatment algorithm we outlined.

The use of medium cutoff dialyzers in patients with multiple myeloma and acute kidney injury requiring hemodialysis: A systematic review

BACKGROUND

Patients with multiple myeloma and high serum levels of circulating free light chains (FLC) have increased risk of acute kidney injury (AKI) secondary to cast nephropathy and is associated with poor survival. Despite removal of FLC by medium cutoff (MCO) dialyzer, the role of MCO hemodialysis (HD) in the treatment of cast nephropathy and its clinical benefits remain unknown.

METHODS

A systematic review was conducted to establish the effectiveness of MCO dialyzer and clinical outcomes, compared to other forms of dialyzers in the removal of FLC, in myeloma patients with AKI. The primary outcome was effectiveness of MCO-HD in reducing serum FLC. The secondary outcomes were HD independence, estimated glomerular filtrate rate, mortality rates, length of hospitalization, rebound of serum FLC before the next dialysis, removal of other molecules during dialysis, and adverse events.

RESULTS

We identified three case series, with a total of 17 patients. There were no randomized controlled trials (RCTs) or cohort studies. These case series showed that MCO dialyzer was effective in the removal of FLC and led to a reduction in FLC concentration post-dialysis. The majority of the case series did not have comparator arm and renal and/or other clinical outcomes.

CONCLUSION

MCO dialyzer appeared to be effective in the removal of FLC based on the existing limited data. However, more data, particularly large-scale RCTs, are needed to assess the use of MCO dialyzer in reducing serum FLC and its effect on clinical outcomes in patients with multiple myeloma and AKI.

High-cutoff hemodialysis in multiple myeloma patients with acute kidney injury

Multiple myeloma (MM), an incurable hematological malignancy with clonal proliferation of plasma cells, is mainly characterized by excessive production of monoclonal immunoglobulins and free light chains (FLCs). Kidney injury is one of the main clinical manifestations and is also a significant predictor of the prognosis of symptomatic MM patients, especially those who require dialysis-supported treatment. Overproduction of FLCs is the trigger for kidney injury, as they can induce the transcription of inflammatory and profibrotic cytokines in the proximal tubule and bind to Tamm-Horsfall protein in the distal tubules to form casts that obstruct the tubules, leading to kidney injury and even renal fibrosis. In addition to traditional antimyeloma treatment, high-cutoff hemodialysis (HCO-HD), which can effectively remove FLCs in vitro, has attracted much attention in recent years. Due to its greater membrane pore size, it has significant advantages in removing larger molecules and can be applied in rhabdomyolysis, sepsis, and even myeloma cast nephropathy. However, mounting questions have recently been raised regarding whether HCO-HD can truly provide clinical benefits in MM patients with acute kidney injury (AKI). Therefore, in this study, we discussed the pathological causes of AKI secondary to MM and summarized the current situation of HCO-HD in MM patients compared with other available extracorporeal techniques. In addition, pivotal clinical trials that reflect the ability of the clearance of FLCs and the side effects of HCO-HD are highlighted, and the relevant protocol of HCO-HD is also provided to assist clinicians in decision-making.

Acute Kidney Injury in Critically Ill Patients with Cancer

Advances in cancer therapy have significantly improved overall patient survival; however, AKI remains a common complication in patients with cancer, occurring in anywhere from 11% to 22% of patients, depending on patient-related or cancer-specific factors. Critically ill patients with cancer as well as patients with certain malignancies (e.g., leukemias, lymphomas, multiple myeloma, and renal cell carcinoma) are at highest risk of developing AKI. AKI may be a consequence of the underlying malignancy itself or from the wide array of therapies used to treat it. Cancer-associated AKI can affect virtually every compartment of the nephron and can present as subclinical AKI or as overt acute tubular injury, tubulointerstitial nephritis, or thrombotic microangiopathy, among others. AKI can have major repercussions for patients with cancer, potentially jeopardizing further eligibility for therapy and leading to greater morbidity and mortality. This review highlights the epidemiology of AKI in critically ill patients with cancer, risk factors for AKI, and common pathologies associated with certain cancer therapies, as well as the management of AKI in different clinical scenarios. It highlights gaps in our knowledge of AKI in patients with cancer, including the lack of validated biomarkers, as well as evidence-based therapies to prevent AKI and its deleterious consequences.

Mono/polyclonal free light chains as challenging biomarkers for immunological abnormalities

Free light chain (FLC) kappa (k) and lambda (λ) consist of low molecular weight proteins produced in excess during immunoglobulin synthesis and secreted into the circulation. In patients with normal renal function, over 99% of FLCs are filtered and reabsorbed. Thus, the presence of FLCs in the serum is directly related to plasma cell activity and the balance between production and renal clearance. FLCs are bioactive molecules that may exist as monoclonal (m) and polyclonal (p) FLCs. These have been detected in several body fluids and may be key indicators of ongoing damage and/or illness. International guidelines now recommend mFLC for screening, diagnosis and monitoring multiple myeloma and other plasma cell dyscrasias. In current clinical practice, FLCs in urine indicate cast nephropathy and other renal injury, whereas their presence in cerebrospinal fluid is important for identifying central nervous system inflammatory diseases such as multiple sclerosis. Increased pFLCs have also been detected in various conditions characterized by B cell activation, i.e., chronic inflammation, autoimmune disease and HCV infection. Monitoring the coronavirus (COVID-19) pandemic by analysis of salivary FLCs presents a significant opportunity in clinical immunology worthy of scientific pursuit.

Light Chain Cast Nephropathy in Multiple Myeloma: Prevalence, Impact and Management Challenges

“Cast nephropathy” (CN) is a pathological feature of myeloma kidney, also seen to a lesser extent in the context of severe nephrotic syndrome from non-haematological diseases. The name relates to obstruction of distal tubules by “casts” of luminal proteins concentrated by intensive water reabsorption resulting from dehydration or high-dose diuretics. Filtered proteins form complexes with endogenous tubular Tamm-Horsfall glycoprotein. The resulting gel further slows or stops luminal flow upon complete obstruction of distal convoluted tubules and collecting ducts. Thus, a tubular obstructive form of acute kidney injury (AKI) is a common consequence of CN. The pathogenesis of CN will be reviewed in light of recent advances in the understanding of monoclonal disorders of B lymphocytes, leading to the release of immunoglobulin components (free light chains, FLC) into the bloodstream and their filtration across the glomerular basement membrane. Treatment aiming at reduction of the circulating burden of FLC may help recovery of renal function in a fraction of these patients, besides filling the void between the onset of AKI, histopathological diagnosis, and full response to pharmacologic treatment.

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Light Chain Restriction in Proximal Tubules-Implications for Light Chain Proximal Tubulopathy

Monoclonal gammopathy (MG) causes various nephropathies, which may suffice for cytoreductive therapy even in the absence of diagnostic criteria for multiple myeloma or B-cell non-Hodgkin lymphoma. The aim of this study was to better understand the significance of light chain (LC) restriction or crystals (LC-R/C) in proximal tubules in the spectrum of LC-induced nephropathies. A consecutive cohort of 320 renal specimens with a history of B-cell dyscrasia was characterized. Special attention was paid to immunohistochemical LC restriction in proximal tubules, tubular crystals or constipation, and ultrastructural findings. Complementary cell culture experiments were performed to assess the role of LC concentrations in generating LC restriction. Light chain restriction or crystals in proximal tubules was found in a quarter of analyzed cases (81/316) and was associated with another LC-induced disease in 70.4% (57/81), especially LC cast-nephropathy (cast-NP) and interstitial myeloma infiltration. LC restriction without significant signs of acute tubular injury was observed in 11.1% (9/81). LC-R/C was not associated with inferior renal function compared to the remainder of cases, when cases with accompanying cast-NP were excluded. Besides crystals, cloudy lysosomes were significantly associated with LC-R/C on an ultrastructural level. In summary, LC-R/C is frequent and strongly associated with cast-NP, possibly indicating that a high load of clonal LC is responsible for this phenomenon, supported by the observation that LC restriction can artificially be generated in cell culture. This and the lack of significant tubular injury in a subgroup imply that in part LC-R/C is a tubular trafficking phenomenon rather than an independent disease process.

Tubulointerstitial nephritis in antineutrophil cytoplasmic antibody-associated vasculitis with monoclonal gammopathy

Isolated tubulointerstitial nephritis (TIN) without glomerular crescent formation is a rare manifestation of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Some patients with monoclonal gammopathy of undetermined significance present with renal complications due to serum monoclonal protein. Here, we present a case of TIN presumably attributable to AAV with monoclonal gammopathy. Laboratory data revealed acute kidney injury, elevated C-reactive protein (CRP) and ANCA titers, and elevated tubular injury markers. Renal biopsy revealed TIN with no apparent glomerular lesion. The findings of peritubular capillaritis and tubulitis indicated that AAV had contributed to the development of TIN. However, in situ hybridization for free light chains revealed kappa light chain restriction, indicating that the involvement of monoclonal gammopathy in the pathogenesis of TIN remains possible. The patient also developed ophthalmic neuropathy, probably caused by AAV. Oral prednisone (0.6 mg/kg/day) administration improved both the ocular symptoms and the laboratory parameters. Our case demonstrated that the concurrence of AAV and monoclonal gammopathy could pose a diagnostic dilemma in distinguishing the cause of TIN. Besides, some reports suggest an association between AAV and monoclonal gammopathy, although direct evidence is lacking. Further research is needed to establish this association.

Treatment of Acute Kidney Injury in Cancer Patients

Acute kidney injury (AKI), either of pre-renal, renal or post-renal origin, is an important complication in cancer patients, resulting in worse prognosis, withdrawal from effective oncological treatments, longer hospitalizations and increased costs. The aim of this article is to provide a literature review of general and cause-specific treatment strategies for AKI, providing a helpful guide for clinical practice. We propose to classify AKI as patient-related, cancer-related and treatment-related in order to optimize therapeutic interventions. In the setting of patient-related causes, proper assessment of hydration status and avoidance of concomitant nephrotoxic medications is key. Cancer-related causes mainly encompass urinary compression/obstruction, direct tumoural kidney involvement and cancer-induced hypercalcaemia. Rapid recognition and specific treatment can potentially restore renal function. Finally, a pre-treatment comprehensive evaluation of risks and benefits of each treatment should always be performed to identify patients at high risk of treatment-related renal damage and allow the implementation of preventive measures without losing the potentialities of the oncological treatment. Considering the complexity of this field, a multidisciplinary approach is necessary with the goal of reducing the incidence of AKI in cancer patients and improving patient outcomes. The overriding research goal in this area is to gather higher quality data from international collaborative studies.

Hypophosphatemia in cancer patients

Dysregulation of phosphorus homeostasis resulting in hypophosphatemia is common in cancer patients and can result in serious complications and impact outcomes. Several factors, including critical illness, nutritional status, cancer type and therapy, influence the development of hypophosphatemia. Hypophosphatemia can develop as a result of phosphaturic mesenchymal tumors or as a paraneoplastic phenomenon. The clinical presentation for hypophosphatemia varies depending on the duration and severity of the hypophosphatemia and affects several organ systems. Among other serious effects, hypophosphatemia can impair tissue oxygenation and can cause hemolysis, leukocyte and platelet dysfunction, encephalopathy, seizures, arrhythmias, cardiomyopathy, rhabdomyolysis and coma. Multiple studies have demonstrated that hypophosphatemia is an adverse prognostic marker in inpatients with increased in-hospital stay, mortality and postoperative complications. The phosphate level is homeostatically regulated and maintained in a narrow range by three main hormones: parathyroid hormone, fibroblast growth factor 23 and 1,25-dihydroxyvitaminD₃. Together, these hormones regulate how the intestine, kidneys and bones traffic phosphorus. Several hematological malignancies and cancer therapies are associated with proximal tubular dysfunction (Fanconi syndrome), resulting in phosphaturia. Caution should be taken with parenteral administration of phosphate salts, because secondary complications can develop, principally due to hypocalcemia. The general approach to hypophosphatemia should target the underlying cause. Early recognition and prevention are essential and the approach to hypophosphatemia in the cancer patient, because of the nuances and complexity, should be multidisciplinary.

Association Between Kidney Function, Proteinuria and the Risk of Multiple Myeloma: A Population-Based Retrospective Cohort Study in South Korea

Purpose

While renal impairment is one of the first clinical manifestations of multiple myeloma (MM), declined renal function may conversely be a risk factor for cancers including MM. In this study, we investigated the relationship between chronic kidney disease and MM at a population level.

Materials and Methods

A total of 9,809,376 adults who participated in a nationwide health screening program and had no MM, cancer or end-stage renal disease at baseline were investigated for incidence of MM. The impact of estimated glomerular filtration rate (eGFR) and random urine dipstick proteinuria, and interactive associations of the two factors on the MM incidence were evaluated.

Results

The general incidence of MM was 4.8 per 100,000 person-years (mean follow-up of 8.3 years). Participants with eGFR < 60 mL/min/1.73 m² (5.8% of participants) had higher MM incidence than those with eGFR ≥ 60 mL/min/1.73 m² (adjusted hazard ratio, 1.29; 95% confidence interval, 1.17 to 1.43). When eGFR was graded into five levels, there was a significant inverse dose-response relationship between eGFR level and MM incidence at the lower eGFR levels (reference: eGFR 60–89 mL/min/1.73 m²). A dose-response relationship was also found with degree of dipstick proteinuria and incidence of MM.

Conclusion

Adults with decreased renal function indicated either by decreased eGFR or presence of proteinuria are at a higher risk of developing MM compared to those without, and there is a dose-response relationship between the severity of renal impairment and MM incidence.

Urinary retinol binding protein predicts renal outcome in systemic immunoglobulin light-chain (AL) amyloidosis

Renal risk stratification in systemic immunoglobulin light-chain (AL) amyloidosis is according to estimated glomerular filtration rate (eGFR) and urinary protein creatinine ratio (uPCR), the latter attributed to glomerular dysfunction, with proximal tubular dysfunction (PTD) little studied. Urinary retinol binding protein 4 (uRBP), a low molecular weight tubular protein and highly sensitive marker of PTD, was prospectively measured in 285 newly diagnosed, untreated patients with systemic AL amyloidosis between August 2017 to August 2018. At diagnosis, the uRBP/creatinine ratio (uRBPCR) correlated with serum creatinine (r = 0·618, P < 0·0001), uPCR (r = 0·422, P < 0·0001) as well as both fractional excretion of phosphate and urate (r = 0·563, P < 0·0001). Log uRBPCR at diagnosis was a strong independent predictor of end-stage renal disease {hazard ratio [HR] 2·65, [95% confidence interval (CI) 1·06-6·64]; P = 0·038}, particularly in patients with an eGFR >30 ml/min/1.73 m2 [HR 4·11, (95% CI 1·45-11·65); P = 0·008] and those who failed to achieve a deep haematological response to chemotherapy within 3 months of diagnosis [HR 6·72, (95% CI 1·83-24·74); P = 0·004], and also predicted renal progression [HR 1·91, (95% CI 1·18-3·07); P = 0·008]. Elevated uRBPCR indicates PTD and predicts renal outcomes independently of eGFR, uPCR and clonal response in systemic AL amyloidosis. The role of uRBPCR as a novel prognostic biomarker merits further study, particularly in monoclonal gammopathies of renal significance.

Cellular antioxidant mechanisms control immunoglobulin light chain-mediated proximal tubule injury

A major cause of morbidity and mortality in multiple myeloma is kidney injury from overproduction of monoclonal immunoglobulin light chains (FLC). FLC can induce damage through the production of hydrogen peroxide, which activates pro-inflammatory and pro-apoptotic pathways. The present study focused on catalase, a highly conserved antioxidant enzyme that degrades hydrogen peroxide. Initial findings were that FLC increased hydrogen peroxide levels but also decreased catalase levels and activity in proximal tubule epithelium. In order to clarify, we showed that the phosphatidylinositol 3-kinase inhibitor, LY294002, inhibited FLC-induced Akt-mediated deactivation of Forkhead box O class 3a (FoxO3a) and increased catalase activity in proximal tubule cells. Augmented catalase activity decreased FLC-mediated production of hydrogen peroxide as well as the associated increase in High Mobility Group Box 1 (HMGB1) protein release and caspase-3 activity. Coincubation of cells with FLC and an allosteric activator of Sirtuin 1 (SIRT1) was also sufficient to increase catalase activity and promote similar cytoprotective effects. Our studies confirmed that the mechanism of downregulation of catalase by FLC involved deactivation of FoxO3a and inhibition of SIRT1. Mechanistic understanding of catalase regulation allows for future treatments that target pathways that increase catalase in the setting of proximal tubule injury from FLC.

Light chain cast nephropathy caused by plasmablastic lymphoma of the bladder

Introduction: Plasmablastic lymphoma (PBL) is a rare form of B-cell lymphoma typically seen in patients with underlying immunosuppression such as HIV, autoimmune disease, and organ transplantation. PBL in HIV-positive patients usually originates from the gastrointestinal tract, with a predilection for the oral cavity. Bladder involvement by PBL is exceedingly rare, and cast nephropathy due to κ light chain-secreting PBL has not been reported previously. Case report: We report a patient who presented with acute kidney injury (AKI) in the setting of HIV, and was found to have a bladder tumor. Bladder pathology revealed a high-grade PBL with κ light chain restriction. Renal biopsy showed κ light chain cast nephropathy, presumably secondary to κ light chain-secreting PBL. Conclusion: Although the prognosis of PBL is poor, our patient recovered from AKI, achieved complete hematologic remission with chemotherapy, and underwent successful autologous stem cell transplant.

The Proximal Tubule Toxicity of Immunoglobulin Light Chains

Plasma and B cells dyscrasias that overproduce monoclonal immunoglobulin free light chains (FLCs) affect the kidney frequently in various ways. The hematologic dyscrasia responsible for the production of FLCs may or may not meet the criteria for cancer, such as multiple myeloma (MM) or lymphoma, or may remain subclinical. If there is overt malignancy, the accompanying kidney disorder is called myeloma- or lymphoma-associated. If the dyscrasia is subclinical, the associated kidney disorders are grouped as monoclonal gammopathy of renal significance. Glomeruli and tubules may both be involved. The proximal tubule disorders comprise a spectrum of interesting syndromes, which range in severity. This review focuses on the recent insights gained into the patterns and the mechanisms of proximal tubule toxicity of FLCs, including subtle transport disorders, such as proximal tubule acidosis, partial or complete Fanconi syndrome, or severe acute or chronic renal failure. Histologically, there may be crystal deposition in the proximal tubule cells, acute tubule injury, interstitial inflammation, fibrosis, and tubule atrophy. Specific structural alterations in the V domain of FLCs caused by somatic hypermutations are responsible for crystal formation as well as partial or complete Fanconi syndrome. Besides crystal formation, tubulointerstitial inflammation and proximal tubulopathy can be mediated by direct activation of inflammatory pathways through cytokines and Toll-like receptors due to cell stress responses induced by excessive FLC endocytosis into the proximal tubule cells. Therapy directed against the clonal source of the toxic light chain can prevent progression to more severe lesions and may help preserve kidney function.

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.

Kidney injury and disease in patients with haematological malignancies

Acute kidney injury (AKI) is common in patients with cancer, especially in those with haematological malignancies. Kidney injury might be a direct consequence of the underlying haematological condition. For example, in the case of lymphoma infiltration or extramedullary haematopoiesis, it might be caused by a tumour product; in the case of cast nephropathy it might be due to the presence of monoclonal immunoglobulin; or it might result from tumour complications, such as hypercalcaemia. Kidney injury might also be caused by cancer treatment, as many chemotherapeutic agents are nephrotoxic. High-intensity treatments, such as high-dose chemotherapy followed by haematopoietic stem cell transplantation, not only increase the risk of infection but can also cause AKI through various mechanisms, including viral nephropathies, engraftment syndrome and sinusoidal obstruction syndrome. Some conditions, such as thrombotic microangiopathy, might also result directly from the haematological condition or the treatment. Novel immunotherapies, such as immune checkpoint inhibitors and chimeric antigen receptor T cell therapy, can also be nephrotoxic. As new therapies for haematological malignancies with increased anti-tumour efficacy and reduced toxicity are developed, the number of patients receiving these treatments will increase. Clinicians must gain a good understanding of the different mechanisms of kidney injury associated with cancer to better care for these patients.

Two kinds of rare light chain cast nephropathy caused by multiple myeloma: case reports and literature review

BACKGROUND

Light chain cast nephropathy (LCCN) is the most common renal disease caused by multiple myeloma (MM). In addition to ordinary light chain protein casts, there are a few rare casts with unique shapes, including light chain amyloid casts (LCAC) and light chain crystal casts (LCCC).

CASE PRESENTATIONS

Here, we report two patients. Patient 1 is a 72-year-old man who was clinically diagnosed with MM and acute kidney injury (AKI). Pathological examination of a renal biopsy revealed that there were many amyloid casts in the distal tubules that had a lightly-stained central area and a deeply-stained burr-like edge. The marginal zone of the cast was positive for Congo red staining and contained numerous amyloid fibers, as observed by electron microscopy. No systemic amyloidosis was found. The patient received 4 courses of bortezomib-based chemotherapy, and then, his MM achieved partial remission. Patient 2 is a 57-year-old man who was also clinically diagnosed with MM and AKI. Pathological examination of a renal biopsy showed that there were many crystalline casts in the distal tubules that were fully or partially composed of crystals with different shapes, including rhomboid, needle, triangle, rectangle and other geometric shapes. Congo red staining was negative. Crystals were also detected in the urine of this patient. After 9 courses of treatment with a bortezomib-based regimen, his MM obtained complete remission and his renal function returned to normal.

CONCLUSIONS

LCAC and LCCC nephropathy caused by MM are two rare types of LCCN, and both have their own unique morphological manifestations. LCAC nephropathy may not be accompanied by systemic amyloidosis. The diagnosis of these two unique LCCNs must rely on renal biopsy pathology, and the discovery of urine crystals is of great significance for indicating LCCC nephropathy.

Renal Expression of Light Chain Binding Proteins

Overproduction of human light chains (LCs) and immunoglobulins can result in various forms of renal disease such as cast nephropathy, monoclonal immunoglobulin deposition disease, LC proximal tubulopathy, AL amyloidosis, and crystal storing histiocytosis. This is caused by cellular uptake of LCs and overwhelmed intracellular transport and degradation in patients with high urine LC concentrations. LC kappa and lambda purification was evaluated by sodium dodecyl sulfate gel electrophoresis. LC and myeloma protein binding to immobilized renal proteins was measured by enzyme-linked immunosorbent assay (ELISA). The human protein microarray (HuProt™) was screened with purified kappa and lambda LC. Identified LC partners were subsequently analyzed in silico for renal expression sites using protein databases, Human Protein Atlas, UniProt, and Bgee. Binding of urinary LCs and immunoglobulins to immobilized whole renal proteins from 22 patients with myeloma or plasma cell dyscrasia was shown by ELISA. Forty lambda and 23 kappa interaction partners were identified from HuProt™ array screens, of which 21 were shared interactors. Among the total of 42 interactors, 12 represented cell surface proteins. Lambda binding signals were approximately 40% higher than kappa signals. LC interaction with renal cells and disease-causing pathologies are more complex than previously thought. It involves an extended spectrum of proteins expressed throughout the nephron, and their identification has been enabled by recently developed methods of protein analysis such as protein microarray screening. Further biochemical studies on interacting proteins are warranted to elucidate their clinical relevance.

Management of acute kidney injury in symptomatic multiple myeloma

Symptomatic multiple myeloma is commonly complicated by acute kidney injury through various mechanisms. The most frequent is the precipitation of monoclonal free light chains with uromodulin in the distal tubules, defining light chain cast nephropathy. Early diagnosis and identification of the cause of acute kidney injury are required for optimizing management and avoiding chronic kidney injury that strongly affects quality of life and patient survival. In light chain cast nephropathy, often manifesting with severe acute kidney injury, renal recovery requires urgent intervention based on vigorous rehydration, correction of precipitating factors, and efficient anti-plasma cell chemotherapy to rapidly reduce the secretion of nephrotoxic free light chains. Currently, the association of the proteasome inhibitor bortezomib with high-dose dexamethasone is the standard regimen in newly diagnosed patients. The addition of another drug such as cyclophosphamide or an immunodulatory agent may improve free light chain response but raises tolerance concerns in frail patients. Further studies are warranted to confirm the role of anti-CD38 monoclonal antibodies, whose efficacy and tolerance have been documented in patients without renal impairment. Despite controversial results from randomized studies, recent data suggest that in patients with light chain cast nephropathy and acute kidney injury requiring dialysis, the combination of chemotherapy with free light chain removal through high-cutoff hemodialysis may increase renal response recovery rates. Kidney biopsy may be helpful in guiding management and assessing renal prognosis that appears to depend on the extent of cast formation and interstitial fibrosis/tubular atrophy. Because of continuous improvement in life expectancy of patients with multiple myeloma, renal transplantation is likely to be increasingly considered in selected candidates.

Effect of high cut-off dialysis for acute kidney injury secondary to cast nephropathy in patients with multiple myeloma: a systematic review and meta-analysis

Background

Acute kidney injury (AKI) caused by cast nephropathy is associated with increased morbidity and mortality among patients with multiple myeloma (MM). High cut-off haemodialysis (HCO-HD) has proven to be effective in the removal of serum light chains but the effect on clinical outcomes, especially renal recovery, remains uncertain.

Methods

A systematic review and meta-analysis were performed examining all randomized controlled trials (RCTs) and observational studies (OBSs) assessing the effect of HCO-HD on clinical outcomes of patients with MM complicated by cast nephropathy–induced severe AKI. The primary outcome was all-cause mortality at the end of the study. The secondary outcomes included all-cause mortality at 12 months, HD independence and serum kappa and lambda light chain reduction. Pooled analysis was performed using random effects models.

Results

We identified five studies, comprising two RCTs and three retrospective cohort studies, including 276 patients with a mean follow-up of 18.7 months. The majority of the studies were of suboptimal quality and underpowered. Compared with patients treated with conventional HD, HCO-HD was not associated with a survival benefit at 12 months {five studies, 276 patients, relative risk [RR] 1.02 [95% confidence interval (CI) 0.76–1.35], I² = 33.9%} or at the end of the studies at an average of 34 months [five studies, 276 patients, RR 1.32 (95% CI 0.71–2.45), I² = 62.0%]. There was no difference in HD independence at 90 days [two trials, 78 patients, RR 2.23 (95% CI 1.09–4.55)], 6 months [two studies, 188 patients, RR 1.19 (95% CI 0.68–2.06)] or 12 months [two studies, 188 patients, RR 1.14 (95% CI 0.58–2.26)]. Patients receiving HCO dialysis, however, had a greater reduction in serum kappa [two studies, 188 patients, weighted mean difference (WMD) 46.7 (95% CI 38.6–54.7), I² =  52.0%] and lambda [two studies, 188 patients, WMD 50.3 (95% CI 21.4–79.3), I² = 95.1%] light chain levels.

Conclusion

Current evidence from RCTs and OBSs suggests HCO dialysis is able to reduce serum free light chains but makes no significant improvement in all-cause mortality and renal outcomes compared with conventional HD for patients with myeloma cast nephropathy. However, there is a trend towards better renal outcomes with the use of HCO dialysis. The lack of long-term data and the small sample sizes of the included studies limit this analysis. Therefore further large-scale RCTs with longer follow-up are needed to assess the effect of HCO dialysis on clinical outcomes in patients with myeloma cast nephropathy.

Monoclonal glomerulopathy with features of cryoglobulinemic glomerulopathy in murine multiple myeloma model

In vivo and animal models of monoclonal light chain-associated renal diseases are limited. The Vk*MYC transgenic model with multiple myeloma in 50-70 weeks old mice with renal involvement has been reported before, but detailed renal pathologic changes have not been well documented. This study fully investigated pathologic changes in the kidneys of Vk*MYC transgenic model using light microscopy, immunofluorescence stains for kappa and lambda light chains, and electron microscopy. Compared to the kidneys of wild-type mice, the kidneys of transgenic mice showed either mesangial segmental expansion, some with associated hypercellularity, and/or thrombotic obstruction of glomerular capillaries. The glomeruli revealed stronger lambda staining than kappa light chain staining. Six out of 12 kidneys from transgenic mice showed abundant electron-dense deposits when examined ultrastructurally. The deposits were located in glomerular capillary lumina in three cases. Large luminal and subendothelial deposits were characterized by randomly disposed microtubular structures measuring up to 16 nm in diameter, with overall features most consistent with cryoglobulins. In summary, about 50% of kidneys from the Vk*MYC mice with myeloma had features most consistent with monoclonal cryoglobulinemic glomerulopathy.

Free light chains injure proximal tubule cells through the STAT1/HMGB1/TLR axis

Free light chains (FLCs) induce inflammatory pathways in proximal tubule cells (PTCs). The role of TLRs in these responses is unknown. Here we present findings on the role of TLRs in FLC-induced PTC injury. We exposed human kidney PTC cultures to κ and λ FLCs and used cell supernatants and pellets for ELISA and gene expression studies. We also analyzed tissues from Stat1-/- and littermate control mice treated with daily i.p. injections of a κ FLC for 10 days. FLCs increased the expression of TLR2, TLR4, and TLR6 via HMGB1, a damage-associated molecular pattern. Countering TLR2, TLR4, and TLR6 through GIT-27 or specific TLR siRNAs reduced downstream cytokine responses. Blocking HMGB1 through siRNA or pharmacologic inhibition, or via STAT1 inhibition, reduced FLC-induced TLR2, TLR4, and TLR6 expression. Blocking endocytosis of FLCs through silencing of megalin/cubilin, with bafilomycin A1 or hypertonic sucrose, attenuated FLC-induced cytokine responses in PTCs. IHC showed decreased TLR4 and TLR6 expression in kidney sections from Stat1-/- mice compared with their littermate controls. PTCs exposed to FLCs released HMGB1, which induced expression of TLR2, TLR4, and TLR6 and downstream inflammation. Blocking FLCs' endocytosis, Stat1 knockdown, HMGB1 inhibition, and TLR knockdown each rescued PTCs from FLC-induced injury.

An update to the pathogenesis for monoclonal gammopathy of renal significance

Monoclonal gammopathy of renal significance (MGRS) is characterized by the nephrotoxic monoclonal immunoglobulin (MIg) secreted by an otherwise asymptomatic or indolent B-cell or plasma cell clone, without hematologic criteria for treatment. The spectrum of MGRS-associated disorders is wide, including non-organized deposits or inclusions such as C3 glomerulopathy with monoclonal glomerulopathy (MIg-C3G), monoclonal immunoglobulin deposition disease, proliferative glomerulonephritis with monoclonal immunoglobulin deposits and organized deposits like immunoglobulin related amyloidosis, type I and type II cryoglobulinaemic glomerulonephritis, light chain proximal tubulopathy, and so on. Kidney biopsy should be conducted to identify the exact disease associated with MGRS. These MGRS-associated diseases can involve one or more renal compartments, including glomeruli, tubules and vessels. Hydrophobic residues replacement, N-glycosylated, increase in isoelectric point in MIg causes it to transform from soluble form to tissue deposition, causing glomerular damage. Complement deposition is found in MIg-C3G, which is caused by an abnormality of the alternative pathway and may involve multiple factors including complement component 3 nephritic factor, anti-complement factor auto-antibodies or MIg which directly cleaves C3. The effect of transforming growth factor beta and platelet-derived growth factor-β on mesangial extracellular matrix is associated with glomerular and tubular basement membrane thickening, nodular glomerulosclerosis, and interstitial fibrosis. Furthermore, inflammatory factors, growth factors and virus infection may play an important role in the development of the diseases. In this review, for the first time, we discussed current highlights in the mechanism of MGRS-related lesions.

An update to the pathogenesis for monoclonal gammopathy of renal significance

Monoclonal gammopathy of renal significance (MGRS) is characterized by the nephrotoxic monoclonal immunoglobulin secreted by an otherwise asymptomatic or indolent B cell or plasma cell clone, without hematologic criteria for treatment. These MGRS-associated diseases can involve one or more renal compartments, including glomeruli, tubules, and vessels. Hydrophobic residue replacement, N-glycosylated, increase in isoelectric point in monoclonal immunoglobulin (MIg) causes it to transform from soluble form to tissue deposition, and consequently resulting in glomerular damage. In addition to MIg deposition, complement deposition is also found in C3 glomerulopathy with monoclonal glomerulopathy, which is caused by an abnormality of the alternative pathway and may involve multiple factors including complement component 3 nephritic factor, anti-complement factor auto-antibodies, or MIg which directly cleaves C3. Furthermore, inflammatory factors, growth factors, and virus infection may also participate in the development of the diseases. In this review, for the first time, we discussed current highlights in the mechanism of MGRS-related lesions.

Immunoglobulin light chains generate proinflammatory and profibrotic kidney injury

Because of the less-than-robust response to therapy and impact on choice of optimal chemotherapy and prognosis, chronic kidney disease has drawn attention in the treatment of multiple myeloma, a malignant hematologic disorder that can produce significant amounts of monoclonal immunoglobulin free light chains (FLCs). These low-molecular-weight proteins are relatively freely filtered through the glomerulus and are reabsorbed by the proximal tubule. The present study demonstrated that during the process of metabolism of immunoglobulin FLCs, ROS activated the STAT1 pathway in proximal tubule epithelium. STAT1 activation served as the seminal signaling molecule that produced the proinflammatory molecule IL-1β, as well as the profibrotic agent TGF-β by this portion of the nephron. These effects occurred in vivo and were produced specifically by the generation of hydrogen peroxide by the VL domain of the light chain. To the extent that the experiments reflect the human condition, these studies offer insights into the pathogenesis of progressive kidney failure in the setting of lymphoproliferative disorders, such as multiple myeloma, that feature increased circulating levels of monoclonal immunoglobulin fragments that require metabolism by the kidney.

Tubular Injury and Dendritic Cell Activation Are Integral Components of Light Chain-Associated Acute Tubulointerstitial Nephritis

CONTEXT.—

Light chain-associated acute tubulointerstitial nephritis (LC-ATIN) is a variant of light chain proximal tubulopathy (LCPT). It is characterized by interstitial inflammation with tubulitis and deposition of monoclonal light chains in the tubulointerstitium. LC-ATIN is a rather poorly recognized pattern of LCPT and not much is known about this entity.

OBJECTIVE.—

To determine the clinicopathologic features of patients with LC-ATIN and investigate the proximal tubular injury and mechanism of interstitial inflammation in LC-ATIN.

DESIGN.—

A total of 38 cases of LC-ATIN were identified from the archives of 5043 renal biopsy specimens. In all cases, routine light microscopic examination, immunofluorescence, and electron microscopic examination were performed. In selected cases, immunofluorescent staining of dendritic cells and immunohistochemical staining for 4 tubular injury markers-KIM-1, p53, bcl-2, and Ki-67-were performed.

RESULTS.—

A characteristic finding in LC-ATIN cases was immunofluorescence staining of monoclonal light chains along tubular basement membranes in linear fashion and inside proximal tubular cells with a granular pattern. No monoclonal light chains were present in glomerular or vascular compartments confirmed with immunofluorescence, electron microscopy, and ultrastructural gold labeling. Ten of 15 LC-ATIN cases (67%) were concurrently positive for the 4 tubular injury markers. Dendritic cells were identified within the tubulointerstitium in the renal biopsy specimens, interacting with surrounding tubules with light-chain deposits and inflammatory cells.

CONCLUSIONS.—

Significant proximal tubular injury occurs associated with LC-ATIN, and the monoclonal light chains accumulated in proximal tubular cells contribute to the injury. Dendritic cells are involved in the pathogenesis of interstitial inflammation in LC-ATIN.

High cutoff versus high-flux haemodialysis for myeloma cast nephropathy in patients receiving bortezomib-based chemotherapy (EuLITE): a phase 2 randomised controlled trial

BACKGROUND

In multiple myeloma, severe acute kidney injury due to myeloma cast nephropathy is caused by pathogenic free light chain immunoglobulin in serum. High cutoff haemodialysis (HCO-HD) can remove large quantities of free light chain immunoglobulin from serum, but its effect on clinical outcomes is uncertain. We therefore aimed to assess whether HCO-HD could increase the frequency of renal recovery in patients with de novo multiple myeloma, severe acute kidney injury, and myeloma cast nephropathy relative to treatment with standard high-flux haemodialysis (HF-HD).

METHODS

In this open-label, phase 2, multicentre, randomised controlled trial (EuLITE), we recruited patients with newly diagnosed multiple myeloma, biopsy-confirmed cast nephropathy, and acute kidney injury that required dialysis from renal services in 16 hospitals in the UK and Germany. Patients were randomly assigned (1:1) by random number generation to receive intensive HCO-HD (in sessions lasting 6-8 h) or standard HF-HD and they were stratified by age and centre. Patients and the medical staff treating them were not masked to treatment allocation. Patients received bortezomib, doxorubicin, and dexamethasone chemotherapy, and were then followed up for 2 years. The primary outcome was independence from dialysis at 90 days after random allocation to groups, which was assessed in an intention-to-treat population. The trial has completed follow-up, and is registered at the ISRCTN registry, number ISRCTN45967602.

FINDINGS

Between June 7, 2008, and Sept 18, 2013, we recruited 90 patients, of whom 43 (48%) were randomly assigned to receive HCO-HD and 47 (52%) were randomly assigned to receive HF-HD. All 90 patients were included in the analysis of the primary outcome. One (2%) patient from the HF-HD group withdrew consent before receiving treatment. During treatment, nine (21%) patients from the HCO-HD group and two (4%) patients in the HF-HD group discontinued trial treatment. After 90 days, 24 (56%) patients in the HCO-HD group and 24 (51%) patients in the HF-HD group were independent from dialysis (relative risk 1·09, 95% CI 0·74-1·61; p=0·81). During the 2-year follow-up, 98 serious adverse events were reported in the HCO-HD group and 82 serious adverse events were reported in the HF-HD group. The most common serious adverse events were infections and adverse events related to the cardiovascular and thrombotic and musculoskeletal systems. During the first 90 days, 26 infections were reported in the HCO-HD group and 13 infections were reported in the HF-HD group, including 14 lung infections in the HCO-HD group and three lung infections in the HF-HD group.

INTERPRETATION

In this phase 2 study, HCO-HD did not improve clinical outcomes for patients with de novo multiple myeloma and myeloma cast nephropathy who required haemodialysis for acute kidney injury and who received a bortezomib-based chemotherapy regimen relative to those receiving HF-HD. These results do not support proceeding to a phase 3 study for HCO-HD in these patients.

FUNDING

Gambro, Janssen, and Binding Site.

Monoclonal gammopathy of renal significance: clinical manifestation, pathogenic characteristic and treatment

Monoclonal gammopathy of renal significance (MGRS) is a group of renal disorders caused by a monoclonal immunoglobulin (MIg) secreted by a dangerous plasmatic/B-cell clone hyperplasia through MIg deposition or dysfunction of complement pathway, with increasing risk of progress to end stage renal disease (ESRD) and the underlying hematologic malignancy. The combination of renal biopsy, complete laboratory examination and bone marrow biopsy is an indispensable diagnostic tool for MGRS to identify accurately and unequivocally the pathogenic monoclonal MIg and provide guidance to treatment. Treatment of MGRS is composed of conventional therapy, chemotherapy, and stem cell transplantation to target the underlying clone and eliminate the noxious MIg on the basis of clinical data of some retrospective studies and a small amount of prospective trial. In addition, it is worthwhile point out assessment of therapeutic effect is significantly relevant for renal and overall prognosis. Thus, by comprehensively analyzing the clinical manifestations and pathogenic characteristic of MGRS, early recognition and prompt treatment can improve the prognosis and prevent post-translation recurrence with multidisciplinary cooperation.

Modeling the Effects of Multiple Myeloma on Kidney Function

Multiple myeloma (MM), a plasma cell cancer, is associated with many health challenges, including damage to the kidney by tubulointerstitial fibrosis. We develop a mathematical model which captures the qualitative behavior of the cell and protein populations involved. Specifically, we model the interaction between cells in the proximal tubule of the kidney, free light chains, renal fibroblasts, and myeloma cells. We analyze the model for steady-state solutions to find a mathematically and biologically relevant stable steady-state solution. This foundational model provides a representation of dynamics between key populations in tubulointerstitial fibrosis that demonstrates how these populations interact to affect patient prognosis in patients with MM and renal impairment.

Lambda Light Chain Non-crystalline Proximal Tubulopathy with IgD Lambda Myeloma

Light Chain Proximal Tubulopathy (LCPT) is a rare form of paraprotein-related kidney disease in which monoclonal free light chains damage the proximal renal tubular epithelial cells. We herein report the case of a 78-year-old woman who presented with anemia and kidney dysfunction. Serum and urine protein electrophoresis analyses revealed a monoclonal IgD and λ free light chains. Proximal tubular injury and the accumulation of λ light chains were found by kidney biopsy. Electron microscopy revealed no organized structure suggestive of crystals. LCPT was caused by IgD lambda myeloma and bortezomib and dexamethasone therapy led to very good partial response (VGPR) without a worsening of the kidney function.

The light at the end of the tunnel: an unusual case of acute kidney injury in a pediatric patient: Answers

Monoclonal gammopathies are a rare diagnosis in pediatric patients. A 19-year-old female patient with past medical history of hypogammaglobulinemia and natural killer cell deficiency and stage III follicular lymphoma, in remission, presented with a right-sided pneumonia, noted to have acute kidney injury and proteinuria. Complement C3 and C4 levels were normal. Anti-double-stranded DNA antibodies, antinuclear antibodies, anti-extractable nuclear antigen antibodies, and antineutrophil cytoplasmic antibodies were negative. A renal biopsy showed numerous fractured tubular casts that were periodic acid-Schiff and silver-stain negative and fuchsinophilic on trichrome stain, with associated giant cells, tubulitis, acute tubular injury, and tubular rupture. The tubular casts had 3+ staining for lambda light chains and 0-1+ staining for kappa light chains. These findings were consistent with light chain cast nephropathy (LCCN). Serum free light chains, serum immunofixation, urine protein electrophoresis, and urine immunofixation studies supported the renal biopsy diagnosis of LCCN. A bone marrow biopsy showed normal trilineage hematopoiesis and also revealed an atypical B cell population detected by flow cytometry. Pathology specimens from lesions in the distal small bowel were characteristic of diffuse large B cell lymphoma (DLBCL). Chemoreduction therapy followed by chemotherapy was initiated for the DLBCL. Three months after initiation of chemotherapy, the patient's creatinine has improved by > 50%. The likely cause of her LCCN was the new diagnosis of a DLBCL. Other risk factors include her history of hypogammaglobulinemia, natural killer (NK) cell deficiency, community-acquired pneumonia, and prior follicular lymphoma. Our patient may be the youngest reported case of LCCN. Treatment of LCCN is based on treating the underlying clonal plasma cell or B cell proliferation, typically with chemotherapy.

Treatment of multiple myeloma with renal involvement: the nephrologist's view

Renal injury is a common complication in multiple myeloma (MM). In fact, as many as 10% of patients with MM develop dialysis-dependent acute kidney injury related to increased free light chain (FLC) production by a plasma cell clone. Myeloma cast nephropathy (MCN) is the most prevalent pathologic diagnosis associated with renal injury, followed by light chain deposition disease and light chain amyloidosis. Several FLC removal techniques have been explored to improve kidney disease in MM but their impact on renal clinical outcomes remains unclear. According to the evidence, high cut-off haemodialysis should be restricted to MM patients on chemotherapy with histological diagnosis of MCN and haemodialysis requirements. From our perspective, more efforts are needed to improve kidney outcomes in patients with MM and renal failure.

Myeloma light chain cast nephropathy, a review

Multiple Myeloma is a plasma cell proliferative disorder that commonly involves the kidney. Renal impairment is a serious complication during the course of the disease that is associated with increased morbidity and mortality. Light chain cast nephropathy is the predominant pattern of renal injury in Multiple Myeloma. This review article focuses on the pathophysiology and diagnostic approach of myeloma cast nephropathy. The management of precipitating factors as well as anti-plasma cell treatment modalities in the context of renal impairment are also discussed.

Dysproteinemias and Glomerular Disease

Dysproteinemia is characterized by the overproduction of an Ig by clonal expansion of cells from the B cell lineage. The resultant monoclonal protein can be composed of the entire Ig or its components. Monoclonal proteins are increasingly recognized as a contributor to kidney disease. They can cause injury in all areas of the kidney, including the glomerular, tubular, and vascular compartments. In the glomerulus, the major mechanism of injury is deposition. Examples of this include Ig amyloidosis, monoclonal Ig deposition disease, immunotactoid glomerulopathy, and cryoglobulinemic GN specifically from types 1 and 2 cryoglobulins. Mechanisms that do not involve Ig deposition include the activation of the complement system, which causes complement deposition in C3 glomerulopathy, and cytokines/growth factors as seen in thrombotic microangiopathy and precipitation, which is involved with cryoglobulinemia. It is important to recognize that nephrotoxic monoclonal proteins can be produced by clones from any of the B cell lineages and that a malignant state is not required for the development of kidney disease. The nephrotoxic clones that do not meet requirement for a malignant condition are now called monoclonal gammopathy of renal significance. Whether it is a malignancy or monoclonal gammopathy of renal significance, preservation of renal function requires substantial reduction of the monoclonal protein. With better understanding of the pathogenesis, clone-directed strategies, such as rituximab against CD20 expressing B cell and bortezomib against plasma cell clones, have been used in the treatment of these diseases. These clone-directed therapies been found to be more effective than immunosuppressive regimens used in nonmonoclonal protein-related kidney diseases.

Paraprotein-Related Kidney Disease: Diagnosing and Treating Monoclonal Gammopathy of Renal Significance

Paraprotein-related kidney disease represents a complex group of diseases caused by an abnormal paraprotein secreted by a clone of B cells. The disease manifestations range from tubulopathies, such as the Fanconi syndrome, to a spectrum of glomerular diseases that can present with varying degrees of proteinuria and renal dysfunction. Diagnosis of these diseases can be challenging because of the wide range of manifestations as well as the relatively common finding of a serum paraprotein, especially in elderly patients. Thus, renal biopsy along with detailed hematologic workup is essential to link the presence of the paraprotein to the associated renal disease. Recent advances in treatment with more effective and targeted chemotherapies, as well as stem cell transplantation, have improved the renal and overall prognosis for many of these disorders.

Paraprotein-Related Kidney Disease: Evaluation and Treatment of Myeloma Cast Nephropathy

Nearly 50% of patients with multiple myeloma develop renal disease, most commonly from AKI caused by cast nephropathy. Development of AKI is associated with poor 1-year survival and reduces the therapeutic options available to patients. There is a great need for more effective therapies. Cast nephropathy is caused by the interaction and aggregation of filtered free light chains and Tamm-Horsfall protein causing intratubular obstruction and damage. The key to treating cast nephropathy is rapid lowering of free light chains, because this correlates with renal recovery. Newer chemotherapy agents rapidly lower free light chains and have been referred to as renoprotective. There is additional great interest in using extracorporeal therapies to remove serum free light chains. Small trials initially showed benefit of therapeutic plasma exchange to improve renal outcomes in cast nephropathy, but a large randomized trial of therapeutic plasma exchange failed to show benefit. A newer technique is extended high-cutoff hemodialysis. This modality uses a high molecular weight cutoff filter to remove free light chains. To date, trials of high-cutoff hemodialysis use in patients with cast nephropathy have been encouraging. However, there are no randomized trials showing the benefit of high-cutoff hemodialysis when used in addition to newer chemotherapeutic regimens. Until these studies are available, high-cutoff hemodialysis cannot be recommended as standard of care.

Paraprotein-Related Kidney Disease: Attack of the Killer M Proteins

Paraproteins are monoclonal Igs or their components (light or heavy chains) that are produced by a clonal population of mature B cells, most commonly plasma cells. These paraproteins or monoclonal proteins are secreted into the blood and subsequently filtered by the glomerulus before entering into urine, where they can cause various types of kidney disease, including both glomerular and tubulointerstitial injuries. Furthermore, a monoclonal protein that causes a specific glomerular or tubulointerstitial lesion in a human can reproducibly cause the same pathology when injected into an animal, supporting unique paraprotein characteristics. This Moving Points in Nephrology will provide an update for the Clinical Journal of the American Society of Nephrology readership on some of the clinically relevant kidney lesions associated with monoclonal paraprotein production and the pathophysiology underlying these kidney lesions.

Paraprotein-Related Kidney Disease: Kidney Injury from Paraproteins-What Determines the Site of Injury?

Disorders of plasma and B cells leading to paraproteinemias are associated with a variety of renal diseases. Understanding the mechanisms of injury and associated nephropathies provides a framework that aids clinicians in prompt diagnosis and appropriate adjunctive treatment of these disorders. Glomerular diseases that may be associated with paraproteinemias include amyloid deposition, monoclonal Ig deposition disease, proliferative GN with monoclonal Ig deposits, C3 glomerulopathy caused by alterations in the complement pathway, immunotactoid glomerulopathy, fibrillary GN, and cryoglobulinemia. Tubular lesions include the classic Fanconi syndrome, light-chain proximal tubulopathy, interstitial fibrosis, and cast nephropathy. These paraproteinemic renal diseases are distinct in their pathogenesis as well as their urinary and kidney biopsy findings. Renal pathology is usually initiated by deposition and direct involvement of the intact monoclonal Ig or Ig fragments with resident cells of the nephron. Our review summarizes current insights into the underlying molecular pathogenesis of these interesting kidney lesions.