Multiple myeloma, nephrotic syndrome and crystalloid inclusions in podocytes

Monoclonal immunoglobulin crystalline nephropathies

Monoclonal Ig crystalline nephropathies are rare lesions resulting from precipitation of monoclonal Igs in the kidney as crystalline inclusions. They can be categorized into lesions with predominant intracellular crystals (light chain [LC] proximal tubulopathy, LC crystal-storing histiocytosis, and LC crystalline podocytopathy) and lesions with predominant extracellular crystals (crystalglobulin-induced nephropathy and crystalline variant of LC cast nephropathy). The majority of these lesions are associated with low tumor burden lymphoproliferative disorders, with the exception of crystalline variant of LC cast nephropathy. Extrarenal involvement (e.g., skin and cornea) is frequent. Kidney biopsy is the cornerstone for diagnosis, which often requires electron microscopy and antigen retrieval. A thorough hematologic workup and evaluation of extrarenal involvement is mandatory for management. Treatment of these lesions is with clone-directed therapy, with the goal of achieving hematologic very good partial response or complete response, which preserves or improves kidney function. In vitro and in vivo studies, animal models, and novel sequencing techniques have been invaluable tools to understand the pathogenesis of LC proximal tubulopathy and can be used to increase our limited knowledge of the pathogenesis of the other monoclonal Ig crystalline nephropathies. This review provides an update on the pathology, renal and hematologic characteristics, extrarenal manifestations, prognosis, treatment, and pathogenesis of monoclonal Ig crystalline nephropathies.

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.

Pathological characteristics of light chain crystalline podocytopathy

Monoclonal immunoglobulin light chain (LC) crystalline inclusions within podocytes are rare, poorly characterized entities. To provide more insight, we now present the first clinicopathologic series of LC crystalline podocytopathy (LCCP) encompassing 25 patients (68% male, median age 56 years). Most (80%) patients presented with proteinuria and chronic kidney disease, with nephrotic syndrome in 28%. Crystalline keratopathy and Fanconi syndrome were present in 22% and 10%, respectively. The hematologic condition was monoclonal gammopathy of renal significance (MGRS) in 55% and multiple myeloma in 45%. The serum monoclonal immunoglobulin was IgG κappa in 86%. Histologically, 60% exhibited focal segmental glomerulosclerosis (FSGS), often collapsing. Ultrastructurally, podocyte LC crystals were numerous with variable effacement of foot processes. Crystals were also present in proximal tubular cells as light chain proximal tubulopathy (LCPT) in 80% and in interstitial histiocytes in 36%. Significantly, frozen-section immunofluorescence failed to reveal the LC composition of crystals in 88%, requiring paraffin-immunofluorescence or immunohistochemistry, with identification of kappa LC in 87%. The LC variable region gene segment, determined by mass spectrometry of glomeruli or bone marrow plasma cell sequencing, was IGKV1-33 in four and IGKV3-20 in one. Among 21 patients who received anti-plasma cell-directed chemotherapy, 50% achieved a kidney response, which depended on a deep hematologic response. After a median follow-up of 36 months, 26% progressed to kidney failure and 17% died. The mean kidney failure-free survival was 57.6 months and was worse in those with FSGS. In sum, LCCP is rare, mostly associates with IgG κappa MGRS, and frequently has concurrent LCPT, although Fanconi syndrome is uncommon. Paraffin-immunofluorescence and electron microscopy are essential to prevent misdiagnosis as primary FSGS since kidney survival depends on early diagnosis and subsequent clone-directed therapy.

Glucocorticoid-dependent Tubulointerstitial Nephritis with IgM-positive Plasma Cells Presenting with Intracellular Crystalline Inclusions within the Rough Endoplasmic Reticulum

Tubulointerstitial nephritis (TIN) with IgM-positive plasma cells (IgMPC-TIN) is an autoimmune kidney disease characterized by IgM/CD138-double-positive plasma cell infiltration in the tubulointerstitium. A 50-year-old man developed IgMPC-TIN and presented with crystalline inclusions in the rough endoplasmic reticulum. Intracellular crystal formation is a rare finding in paraprotein-related kidney diseases, but this case showed no pathogenic monoclonal immunoglobulin. Prednisolone (PSL, 30 mg) improved the TIN, but PSL tapering resulted in the recurrence of TIN. Combination therapy with 15 mg PSL and 150 mg mizoribine ultimately stabilized TIN. This case offers original evidence concerning the pathophysiology and treatment strategy of IgMPC-TIN.

Crystal-Induced Podocytopathy Producing Collapsing Focal Segmental Glomerulosclerosis in Monoclonal Gammopathy of Renal Significance: A Case Report

Monoclonal gammopathy–associated crystalline podocytopathy causing collapsing focal segmental glomerulosclerosis (FSGS) is very rare and has been associated with pamidronate therapy. We present the case of a 53-year-old man with vision loss secondary to corneal crystals deposition, nephrotic-range proteinuria, and reduced glomerular filtration rate without associated comorbid conditions. Two kidney biopsies were initially reported as primary FSGS but the patient did not respond to high-dose corticosteroid immunosuppression therapy. Repeat review of biopsies with additional electron microscopy analysis revealed crystalline inclusions in podocytes leading to collapsing FSGS. Subsequent workup revealed an immunoglobulin G κ serum monoclonal protein. Bone marrow biopsy revealed 5% κ-restricted plasma cells with cytoplasmic crystalline inclusions. To our knowledge, this is the first case of monoclonal gammopathy of clinical significance manifesting as crystalline podocytopathy leading to collapsing FSGS and keratopathy leading to vision loss. Crystalline podocytopathy should be considered in the differential diagnosis of collapsing glomerulopathy, and careful ultrastructural examination of the kidney biopsy specimen is crucial to establish this diagnosis.

Crystals, crystals everywhere but not a clue till late… Light chain crystalline proximal tubulopathy with concomitant myeloma cast nephropathy

The renal diseases commonly associated with myeloma include primary amyloidosis, cast nephropathy, and light chain deposition disease. Less frequent forms of renal involvement encountered in the course of myeloma are crystalline and non-crystalline proximal tubulopathies, neoplastic plasma cell infiltration, and immunoglobulin crystallization in interstitial histiocytes and glomerular cells including podocytes. Light chain proximal tubulopathy (LCPT) caused by aggregation of non-crystalline and rarely crystalline deposits of monoclonal light chains in the cytoplasm of proximal tubular epithelial cells, accounts for less than 5% of monoclonal gammopathy-associated kidney diseases. We report the case of a 48-year-old Indian woman with multiple myeloma, who presented with acute kidney injury and nephrotic syndrome, in whom the renal biopsy revealed widespread crystalline inclusions in extraglomerular and glomerular compartments. We present illustrative light microscopic (LM) and diagnostic electron microscopic (EM) findings of this case which enabled a diagnosis of crystalline LCPT, crystal storing histiocytosis, and crystalline podocytopathy occurring synchronously with myeloma cast nephropathy. While documenting this unique juxtapositioning of multicompartmental paraproteinemic renal injury in multiple myeloma, diagnosed after EM analysis of the patient's renal biopsy, we discuss the pathogenetic pathways of this condition along with the clinical implications. Due to intrinsic structural properties of the crystals, they frequently escape detection by routine LM, necessitating EM analysis for their diagnosis. Given the prognostic implications of tubulopathies complicating myeloma, LCPT is a critically important diagnosis, highlighting the need for a comprehensive renal biopsy evaluation inclusive of EM for the practice of precision medicine in such scenarios.

Crystalline deposits in the cornea and various areas of the kidney as symptoms of an underlying monoclonal gammopathy: a case report

Background

Plasma cell dyscrasias (PCD) are characterized by an abnormal production of intact monoclonal immunoglobulins or parts such as heavy or light chains. In most cases, the monoclonal protein (also termed paraprotein) is produced by a clonal plasma cell population. The production of monoclonal proteins can result in deposits of various types and localization depending on the type, amount, and electrochemical properties of the paraprotein. One histopathologic presentation, albeit rare, are crystalline deposits. They can form in various organs and hence cause a wide spectrum of symptoms.

Case presentation

A 49-year-old man presented to the emergency department with eyestrain and foreign body sensation after overhead drilling. Examination of the eyes revealed crystalline deposits in the cornea of both eyes. After additional diagnostic testing, deposits were attributed to free light chains. Monoclonal gammopathy of undetermined significance (MGUS) was diagnosed according to serum electrophoresis and immunofixation. Four years later, new onset of proteinuria was detected. A percutaneous biopsy of the kidney showed severe light chain podocytopathy with secondary focal segmental glomerulosclerosis (FSGS) and light chain proximal tubulopathy (LCPT). In these lesions, crystalline deposits identical to the corneal deposits were found in ultrastructural and immunofluorescent analysis. The patient was diagnosed with monoclonal gammopathy of renal significance (MGRS), and a plasma cell directed therapy was initiated.

Conclusions

PCD can present with a wide array of symptoms and are notoriously difficult to diagnose. Extrarenal manifestations such as crystalline deposits in the cornea are one possible manifestation. The case presented herein emphasizes the notion that extrarenal paraprotein deposits warrant a thorough search for the underlying clonal disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02309-x.

Bisphosphonates to reduce bone fractures in stage 3B+ chronic kidney disease: a propensity score-matched cohort study

BACKGROUND

Bisphosphonates are contraindicated in patients with stage 4+ chronic kidney disease. However, they are widely used to prevent fragility fractures in stage 3 chronic kidney disease, despite a lack of good-quality data on their effects.

OBJECTIVES

The aims of each work package were as follows. Work package 1: to study the relationship between bisphosphonate use and chronic kidney disease progression. Work package 2: to study the association between using bisphosphonates and fracture risk. Work package 3: to determine the risks of hypocalcaemia, hypophosphataemia, acute kidney injury and upper gastrointestinal events associated with using bisphosphonates. Work package 4: to investigate the association between using bisphosphonates and changes in bone mineral density over time.

DESIGN

This was a new-user cohort study design with propensity score matching.

SETTING AND DATA SOURCES

Data were obtained from UK NHS primary care (Clinical Practice Research Datalink GOLD database) and linked hospital inpatient records (Hospital Episode Statistics) for work packages 1-3 and from the Danish Odense University Hospital Databases for work package 4.

PARTICIPANTS

Patients registered in the data sources who had at least one measurement of estimated glomerular filtration rate of < 45 ml/minute/1.73 m2 were eligible. A second estimated glomerular filtration rate value of < 45 ml/minute/1.73 m2 within 1 year after the first was requested for work packages 1 and 3. Patients with no Hospital Episode Statistics linkage were excluded from work packages 1-3. Patients with < 1 year of run-in data before index estimated glomerular filtration rate and previous users of anti-osteoporosis medications were excluded from work packages 1-4.

INTERVENTIONS/EXPOSURE

Bisphosphonate use, identified from primary care prescriptions (for work packages 1-3) or pharmacy dispensations (for work package 4), was the main exposure.

MAIN OUTCOME MEASURES

Work package 1: chronic kidney disease progression, defined as stage worsening or starting renal replacement. Work package 2: hip fracture. Work package 3: acute kidney injury, hypocalcaemia and hypophosphataemia identified from Hospital Episode Statistics, and gastrointestinal events identified from Clinical Practice Research Datalink or Hospital Episode Statistics. Work package 4: annualised femoral neck bone mineral density percentage change.

RESULTS

Bisphosphonate use was associated with an excess risk of chronic kidney disease progression (subdistribution hazard ratio 1.12, 95% confidence interval 1.02 to 1.24) in work package 1, but did not increase the probability of other safety outcomes in work package 3. The results from work package 2 suggested that bisphosphonate use increased fracture risk (hazard ratio 1.25, 95% confidence interval 1.13 to 1.39) for hip fractures, but sensitivity analyses suggested that this was related to unresolved confounding. Conversely, work package 4 suggested that bisphosphonates improved bone mineral density, with an average 2.65% (95% confidence interval 1.32% to 3.99%) greater gain in femoral neck bone mineral density per year in bisphosphonate users than in matched non-users.

LIMITATIONS

Confounding by indication was a concern for the clinical effectiveness (i.e. work package 2) data. Bias analyses suggested that these findings were due to inappropriate adjustment for pre-treatment risk. work packages 3 and 4 were based on small numbers of events and participants, respectively.

CONCLUSIONS

Bisphosphonates were associated with a 12% excess risk of chronic kidney disease progression in participants with stage 3B+ chronic kidney disease. No other safety concerns were identified. Bisphosphonate therapy increased bone mineral density, but the research team failed to demonstrate antifracture effectiveness.

FUTURE WORK

Randomised controlled trial data are needed to demonstrate antifracture efficacy in patients with stage 3B+ chronic kidney disease. More safety analyses are needed to characterise the renal toxicity of bisphosphonates in stage 3A chronic kidney disease, possibly using observational data.

STUDY REGISTRATION

This study is registered as EUPAS10029.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 17. See the NIHR Journals Library website for further project information. The project was also supported by the National Institute for Health Research Biomedical Research Centre, Oxford.

Safety of Intravenous Bisphosphonates for the Treatment of Hypercalcemia in Patients With Preexisting Renal Dysfunction

BACKGROUND

Although intravenous (IV) bisphosphonates are first-line medications for the management of hypercalcemia, studies examining their use in patients with preexisting renal dysfunction are limited.

OBJECTIVE

The objective of this study is to describe the safety and efficacy of pamidronate and zoledronic acid in the treatment of hypercalcemia in patients with baseline renal dysfunction.

METHODS

A retrospective analysis was conducted of IV pamidronate and zoledronic acid in adult patients with hypercalcemia and creatinine clearance (CrCl) <60 mL/min. The primary endpoint was incidence of all-grade serum creatinine (SCr) elevations. Secondary endpoints included refractory hypercalcemia, hypocalcemia, osteonecrosis of the jaw (ONJ), corrected serum calcium (CSC) decrease ≥1.0 mg/dL by day 7 of bisphosphonate administration, and normalization of CSC ≤10.5 mg/dL by days 10 and 30.

RESULTS

A total of 113 patients were included (n = 55 pamidronate, n = 58 zoledronic acid). The primary endpoint of all-grade SCr elevation occurred in 28 (24.8%) patients. Grades 3/4 SCr elevations occurred in 10.9% of patients treated with pamidronate and 1.7% of patients receiving zoledronic acid. Approximately 16% and 14% of patients developed grades 1 and 2 hypocalcemia, respectively, and there were no cases of ONJ. Overall, 64.6% of patients achieved normalization of CSC by day 10, and there were no statistical differences between bisphosphonate type and renal function.

CONCLUSIONS AND RELEVANCE

The analysis suggests an association between IV bisphosphonates and increased rates of SCr elevations among patients with preexisting renal dysfunction. Future prospective studies are necessary to elucidate these findings.

A case report of crystalline light chain inclusion-associated kidney disease affecting podocytes but without Fanconi syndrome: A clonal analysis of pathological monoclonal light chain

RATIONALE

Crystalline light chain inclusion-associated kidney disease affects mainly tubular epithelial cells and is often clinically manifested as Fanconi syndrome. However, only very few case reports about the crystalline deposits within the podocytes are available, and the nature of the pathogenic monoclonal light chain implicated in these cases is still unknown. We report a case of crystalline inclusion-associated kidney disease manifested as crystalline podocytopathy in which we identified the complete structure of the pathogenic monoclonal light chain as belonging to the germ-line gene of Vκ1-39.

PATIENT CONCERNS

We describe a 65-year-old woman with crystalline light chain inclusion-associated kidney disease showing mild proteinuria and renal insufficiency with monoclonal gammopathy of undetermined significance without Fanconi syndrome. She had crystalline inclusions mainly within podocytes, tubular epithelial cells and histiocytes in the kidney. Light microscopy showed vacuolation of podocytes and tubular epithelial cells, while eosin negative pale needle-like crystals were present within these cells. Electron microscopy showed accumulation of club-like crystals with high electron density in podocytes, proximal tubular epithelial cells and interstitial histiocytes. Clonal analysis revealed that a pathogenic monoclonal light chain was derived from germline gene, Vκ1-39.

DIAGNOSES

The diagnosis of crystalline light chain inclusion-associated kidney disease was made.

INTERVENTIONS AND OUTCOMES

Bortezomib and dexamethasone were started and her renal function improved to eGFR 36 mL/min/1.73 m after 9 courses of therapy.

LESSONS

Patients with light chain crystalline podocytopathy may have a similar pathogenic monoclonal light chain derived from the same germline gene, Vκ1-39, to that of patients with light chain proximal tubulopathy.

Multiple myeloma with crystal-storing histiocytosis, crystalline podocytopathy, and light chain proximal tubulopathy, revealed by retinal abnormalities: A case report

RATIONALE

Crystal sorting histiocytosis (CSH) is a rare disorder that is morphologically characterized by the accumulation of monoclonal immunoglobulin crystals, predominantly of a kappa light chain type, within lysosomes of macrophages. CSH may result in a variety of clinical manifestations depending on the involved organs. In this case report, we aim to describe a patient with ophthalmic manifestations which lead to the diagnosis of multiple myeloma with crystal-storing histiocytosis, crystalline podocytopathy, and light chain proximal tubulopathy.

PATIENT CONCERNS

A 60-year-old male patient presented with progressive bilateral decreased vision for 2 years.

DIAGNOSIS

Ophthalmic explorations showed bilateral macular and papillary edema, and multiple crystalline deposits in the anterior stromal cornea and in the retina. Laboratory tests showed nephrotic syndrome and renal dysfunction. Further work-up revealed IgG kappa multiple myeloma, with biopsy-proven combined crystalline podocytopathy and tubulopathy.

INTERVENTIONS

The patient received chemotherapy (bortezomib, cyclophosphamide, and dexamethasone for 3 cycles, then bortezomib, lenalidomide, and dexamethasone).

OUTCOMES

Despite partial hematologic response and improvement of the papilledema and macular edema, the patient developed dialysis-dependent end-stage renal failure.

LESSONS

This report, highlighting the protean presentation of paraprotein-mediated injuries, provides additional information on the ocular anomalies not previously described that may be associated with crystal-storing histiocytosis.

Monoclonal light chain crystalline podocytopathy and tubulopathy associated with monoclonal gammopathy of renal significance: a case report and literature review

Background

Monoclonal gammopathy of renal significance (MGRS) is a recently defined group of renal diseases caused by monoclonal immunoglobulin secreted by nonmalignant proliferative B cell or plasma cell. Monoclonal immunoglobulin can form different types of structures deposited in renal tissue, including fibrils, granules, microtubules, crystals and casts, and has mostly been reported in multiple myeloma patients. Here we report a rare case with κ light chain crystals in both podocytes and tubular epithelial cells associated with MGRS, which adds more information to the spectrum of MGRS-related renal diseases.

Case presentation

A 53-year old woman presented with albumin–predominant moderate proteinuria and renal failure. She had monoclonal IgGκ in the serum and monoclonal IgGκ plus free κ in the urine. Multiple myeloma and lymphoproliferative disorders were excluded. Renal biopsy confirmed κ-restricted crystal-storing renal disease involving the podocytes and proximal tubular epithelial cells. The patient was treated with bortezomib followed by lenalidomide-based chemotherapy, and renal function was stable after 1 year of follow-up.

Conclusions

This is a rare case of combined crystalline podocytopathy and tubulopathy associated with MGRS, in which diagnosis was dependent on electron and immuno-electron microscopy.

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.

Isolated Crystalloid Podocytopathy With Focal Segmental Glomerulosclerosis in Renal Allograft: An Unusual Presentation of Post-Transplant Monoclonal Gammopathy of Renal Significance-A Case Report

BACKGROUND

Monoclonal gammopathy of renal significance denotes a spectrum of hematologic disorders that cause direct or indirect renal damage.

CASE PRESENTATION

A 51-year-old man had received a living-donor kidney transplant from his wife in 2008. He had gradual increased proteinuria 4 years later. His renal biopsy results revealed cytoplasmic crystalloid inclusions in the podocytes. No crystalloid inclusion was found in other renal cells. Despite that immunofluorescent examination failed to show light-chain deposition, the serum immuno-electrophoresis revealed monoclonal immunoglobulin-Gκ. Bone marrow biopsy showed interstitial infiltration of plasma cells of approximately 10%. A follow-up renal biopsy was performed in 2016. Light microscopy showed focal segmental glomerulosclerosis. The immunofluorescent examination remained negative for light chain, but κ-light chain could be demonstrated after antigen retrieval. Similar to previous biopsy results, cytoplasmic inclusions were found only in podocytes without involving other renal cells.

CONCLUSIONS

To the best of our knowledge, this is the first report of monoclonal gammopathy of renal significance presenting as isolated crystalloid podocytopathy in the allograft kidney. The mechanism of preferential podocyte deposition of crystalloid immunoglobulin remains unclear. The inherent features of crystalloid podocytopathy may mislead the pathologic diagnosis.

Light Chain Podocytopathy Mimicking Recurrent Focal Segmental Glomerulosclerosis

Kidney injury related to paraproteinemia is common and typically occurs after the fourth decade of life in association with an underlying plasma cell dyscrasia or other lymphoproliferative disease. Kidney transplantation in paraprotein-related kidney disease can be successful in conjunction with treatment of the underlying hematopoietic process; however, when hematologic response to therapy is not achieved, recurrent kidney injury is frequently seen. We describe a young male patient who presented at the age of 23 years with end-stage kidney disease thought to be secondary to focal segmental glomerulosclerosis; this patient ultimately received two kidney allografts. He experienced recurrent proteinuria in both kidneys, with a biopsy from his second allograft showing kappa-restricted crystalline light chain podocytopathy, which was identified in both his native and first allograft kidneys upon retrospective review. Recurrent light chain podocytopathy has not been previously reported but poses a diagnostic challenge as it can mimic focal segmental glomerulosclerosis, particularly in young patients in whom paraprotein-related kidney injury is usually not suspected.

Crystalline podocytopathy and tubulopathy without overt glomerular proteinuria in a patient with multiple myeloma

Crystalline nephropathy is a rare yet well-known condition associated with multiple myeloma and other light chain–secreting disorders. Paraproteins that are resistant to proteolysis crystallize within proximal tubular cells and cause light-chain proximal tubulopathy, which presents clinically as Fanconi syndrome. Podocytes are rarely affected, and the crystalline inclusions within podocytes are typically precipitated, yielding significant glomerular proteinuria. Here we report a case of extensive crystalline inclusions primarily within podocytes and proximal tubules that presented only with Fanconi syndrome and renal insufficiency. Despite the presence of extensive crystalline inclusions in podocytes and diffuse foot process effacement, the patient had no clinical evidence suggestive of podocyte injury.

Renal Light Chain Deposition Associated with the Formation of Intracellular Crystalline Inclusion Bodies in Podocytes: A Rare Case Report

We herein report the case of an elderly woman with bone pain and proteinuria as the main clinical manifestations. The patient was diagnosed with the IgG κ type of multiple myeloma. Her renal pathology consisted of widespread κ light chain protein deposition associated with the formation of large quantities of rod-like crystals in podocytes. This phenomenon is very rare. We explored the significance of this crystal formation via a detailed and descriptive analysis and also performed a literature review, thus providing data to increase the available information about this type of disease.

Crystalloid podocytopathy with focal segmental glomerulosclerosis in PCM: a case report

Background

Crystalloid podocytopathy with focal segmental glomerulosclerosis in plasma cell myeloma (PCM) is rare.

Case Presentation

We present a case of crystalline deposition in the bone marrow (BM) and various renal cells with only proteinuria as a symptom. As workup for proteinuria, a renal biopsy sample was obtained. EM showed multiple crystalline depositions in renal tubular cells and podocytes. Focal segmental glomerulosclerosis with crystalloid podocytopathy was diagnosed. Because monoclonal gammopathy was detected in the serum and urine, a BM study was also performed. Plasma cells with needle-shaped inclusion bodies were observed. The crystalline deposits in the plasma cells and podocytes were positive for Masson’s trichrome and kappa light-chain staining. These findings indicated that the crystalline deposits originated from paraprotein. The case showed a rare process of focal segmental glomerulosclerosis via crystalline deposition in podocytes in plasma cell myeloma.

Conclusions

Crystalloid podocytopathy is a likely cause of renal damage such as FSGS in PCM, although it is an uncommon mechanism for myeloma kidney.

Light Chain Proximal Tubulopathy: Clinical and Pathologic Characteristics in the Modern Treatment Era

Light chain proximal tubulopathy (LCPT) is characterized by cytoplasmic inclusions of monoclonal LC within proximal tubular cells. The significance of crystalline versus noncrystalline LCPT and the effect of modern therapies are unknown. We reported the clinical-pathologic features of 40 crystalline and six noncrystalline LCPT patients diagnosed between 2000 and 2014. All crystalline LCPTs were κ-restricted and displayed acute tubular injury. One-third of noncrystalline LCPT patients displayed λ-restriction or acute tubular injury. Only crystalline LCPT frequently required antigen retrieval to demonstrate monoclonal LC by immunofluorescence. In five of 38 patients, crystals were not detectable by light microscopy, but they were visible by electron microscopy. Hematolymphoid neoplasms, known before biopsy in only 15% of patients, included 21 monoclonal gammopathies of renal significance; 15 multiple myelomas; seven smoldering multiple myelomas; and three other neoplasms. Biopsy indications included Fanconi syndrome (38%; all with crystalline LCPT), renal insufficiency (83%), and proteinuria (98%). Follow-up was available for 30 (75%) patients with crystalline LCPT and all six patients with noncrystalline LCPT, of whom 11 underwent stem cell transplant, 16 received chemotherapy only, and nine were untreated. Complete or very good partial hematologic remissions occurred in six of 22 treated crystalline LCPT patients. By multivariable analysis, the only independent predictor of final eGFR was initial eGFR, highlighting the importance of early detection. All patients with crystalline LCPT treated with stem cell transplant had stable or improved kidney function, indicating the effectiveness of aggressive therapy in selected patients.

Multiple myeloma with a previous diagnosis of focal segmental glomerulosclerosis: A case report and review of the literature

The presentation of focal segmental glomerulosclerosis (FSGS) and multiple myeloma (MM), either together or in succession, is extremely rare. Only nine studies have previously reported this poorly understood association. The present study reports the case of a 45-year-old male with FSGS that was diagnosed by a renal biopsy performed for nephrotic syndrome (NS). The patient was admitted to the Chinese People's Liberation Army General Hospital one year later with a fever, anemia, unresolved NS and renal insufficiency. The patient was diagnosed with MM and a renal biopsy was repeated, the results of which suggested renal amyloidosis. The MM was treated with three cycles of vincristine, doxorubicin and dexamethasone chemotherapy. A review of the literature indicated that monoclonal gammopathy may lead to FSGS. It suggested that FSGS patients who are >40 years old should be routinely screened for plasma cell proliferative disorders to guide the treatment, determine a prognosis, achieve primary disease remission and avoid end-stage renal disease.

Crystalloid glomerulopathy in monoclonal gammopathy of renal significance (MGRS)

We report a case of monoclonal gammopathy of renal significance in a 63-year-old man who presented with nephrotic-range proteinuria and renal insufficiency. The kidney biopsy showed a membranoproliferative glomerulonephritis pattern with extensive crystalloid deposits in the glomerular capillary endothelial cells and very few in the tubular epithelial cells. The immunoperoxidase staining showed kappa light chain restriction. Subsequently, the bone marrow showed 6% plasma cells which confirmed the diagnosis of monoclonal gammopathy of renal significance. He responded well to bortezomib treatment with resolution of the nephrotic syndrome and normalization of renal function after 7 months.

Combined crystalline podocytopathy and tubulopathy associated with multiple myeloma

Lymphoplasmacytic neoplasms cause a wide range of injuries to the kidney exemplified by light chain cast nephropathy and amyloidosis. Filtered paraproteins can also accumulate within kidney cells and cause direct cytotoxic injury. Rarely, paraproteins that are resistant to proteolysis can crystallize within proximal tubules and cause acute tubular injury. In contrast, accumulation of crystallized paraproteins in other kidney cells, especially podocytes, is exceptional. Here, we report the finding of crystalline inclusions within podocytes and proximal tubules in a patient who presented with a combined nephrotic syndrome and Fanconi syndrome. Further workup revealed previously unsuspected multiple myeloma and elevated serum free light chains, highlighting the protean presentation of paraprotein-mediated injuries to the kidney.

Light Chain Proximal Tubulopathy: Expanding the Pathologic Spectrum with and without Deposition of Crystalline Inclusions

Light chain proximal tubulopathy (LCPT) is an uncommon form of renal disease associated with dysproteinemias. It is characterized by intracytoplasmic deposition of crystallized mostly kappa monoclonal light chains in proximal tubules (PTs). Crystals are located within lysosomes by electron microscopy (EM). Rare lambda LCPT cases without crystals by EM were described. Retrospectively, we reviewed clinical, light microscopic (LM), immunofluorescence (IF), and EM findings in 9 cases) (8 males, 1 female; mean age 57 years (38–81)) with multiple myeloma. LM showed abundant cytoplasmic droplets in PT cells in all cases. Droplets were also present in the podocytes, endothelial and parietal cells in one case. IF revealed staining of crystals with kappa in 3 and lambda in 6. EM showed electron dense rectangular, rhomboid, or needle shaped crystals in PT cells in 3 cases (33%), one of which had crystals in podocytes and interstitial cells. Six lambda LCPT cases showed no crystals by EM (67%). This may reflect differences in the physicochemical properties of light chains. The mechanisms of crystal accumulation in these cells and the significance of this finding are unknown.

[Bisphosphonate-induced collapsing focal segmental glomerulosclerosis; two clinical cases and literature review]

Collapsing focal segmental glomerulosclerosis is well described in its idiopathic form, mostly seen in young African American patients, and in association with HIV virus. Its clinical presentation typically includes proteinuria and renal failure rapidly progressing to end stage renal disease. However, a new form has recently been described related to treatment with high doses of intravenous bisphosphonates, especially pamidronate. We report two cases of collapsing focal segmental glomerulosclerosis in patients treated with intravenous pamidronate. In opposition to previous reports, interruption of pamidronate administration did not improve renal function. The latter should be evaluated before initiating treatment with bisphosphonates and regularly monitored. For patients with chronic kidney disease, introduction of bisphosphonates should be reconsidered given the risk of rapid progression to end stage renal disease and the lack of evidence for reduction of fracture risk in this population.

Bisphosphonate nephrotoxicity

Bisphosphonates are valuable agents for the treatment of post-menopausal osteoporosis (PMO), hypercalcemia of malignancy, and osteolytic bone metastases. Oral bisphosphonates are used mainly to treat PMO and are not associated with significant nephrotoxicity. In contrast, nephrotoxicity is a significant potential limiting factor to the use of intravenous (IV) bisphosphonates, and the nephrotoxicity is both dose-dependent and infusion time-dependent. The two main IV bisphosphonates available to treat hypercalcemia of malignancy and osteolytic bone disease in the United States are zoledronate and pamidronate. Patterns of nephrotoxicity described with these agents include toxic acute tubular necrosis and collapsing focal segmental glomerulosclerosis, respectively. With both of these agents, severe nephrotoxicity can be largely avoided by stringent adherence to guidelines for monitoring serum creatinine prior to each treatment, temporarily withholding therapy in the setting of renal insufficiency, and adjusting doses in patients with pre-existing chronic kidney disease. In patients with PMO, zoledronate and pamidronate are associated with significantly less nephrotoxicity, which undoubtedly relates to the lower doses and longer dosing intervals employed for this indication. Ibandronate is approved in the US for treatment of PMO and in Europe for treatment of PMO and malignancy-associated bone disease. Available data suggest that ibandronate has a safe renal profile without evidence of nephrotoxicity, even in patients with abnormal baseline kidney function.

The spectrum of podocytopathies: a unifying view of glomerular diseases

Glomerular diseases encompass a broad array of clinicopathologically defined syndromes which together account for 90% of end-stage kidney disease costing $20 billion per annum to treat in the United States alone. Recent insights have defined the central role of the podocyte as both the regulator of glomerular development as well as the determinant of progression to glomerulosclerosis. We can now place all glomerular diseases within this spectrum of podocytopathies with predictable outcomes based on podocyte biology impacted by temporal, genetic, and environmental cues. This simplified construct is particularly useful to rationalize clinical effort toward podocyte preservation and prevention of progression as well as to focus basic research effort on understanding podocyte biology and for clinical research toward development of practical monitoring strategies for podocyte injury, dysfunction, and loss.