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.

Incidence and Risk Factors for Acute and Chronic Kidney Injury after Adult Cord Blood Transplantation.

Although cord blood transplantation (CBT) extends allograft access, patient comorbidities, chemoradiation, and nephrotoxic medications all contribute to acute kidney injury (AKI) risk. We analyzed AKI in adult myeloablative CBT recipients who underwent transplantation from 2006 to 2017 for hematologic malignancies using cyclosporine A (CSA)/mycophenolate mofetil immunosuppression. Maximum grades of AKI were calculated using Kidney Disease: Improving Global Outcomes (grade 1, 1.5 to <2-fold; grade 2, 2 to <3-fold; or grade 3, ≥3-fold over baseline) definitions. In total, 153 patients (median 51 years [range, 23-65], 114/153 [75%] acute leukemia, 27/153 [18%] African, 88/153 [58%] cytomegalovirus seropositive, median age-adjusted hematopoietic cell comorbidity index 3 [range, 0-9], median pretransplant albumin 4.0 g/dL [range, 2.6-5.2]) underwent transplantation. The day 100 cumulative incidence of grade 1-3 AKI was 83% (95% confidence interval [CI], 77%-89%) (predominantly grade 2, median onset 40 days, range 0 to 96), and grade 2-3 AKI incidence was 54% (95% CI, 46%-62%) (median onset 43 days, range 0 to 96). Mean CSA level preceding AKI onset was high (360 ng/mL, target range 300-350). In multivariate analysis, African ancestry, addition of haploidentical CD34+ cells, low day -7 albumin, critical illness/intensive care admission, and nephrotoxic drug exposure (predominantly CSA and/or foscarnet) were associated with AKI. In a day 100 landmark analysis, 6% of patients with no prior AKI had chronic kidney disease (CKD) at 2 years versus 43% with prior grade 1 and 38% with prior grade 2-3 AKI (overall P= .02). Adult CBT recipients are at significant AKI risk, and AKI is associated with increased risk of CKD. Prevention strategies, early recognition, and prompt intervention are critical to mitigate kidney injury.

The sensitivity and specificity of the routine kidney biopsy immunofluorescence panel are inferior to diagnosing renal immunoglobulin-derived amyloidosis by mass spectrometry.

Immunoglobulin light chain amyloidosis is the most frequent type of renal amyloidosis in the United States, accounting for 81% of cases. Accurate typing is crucial for early diagnosis and treatment of immunoglobulin-derived amyloidosis and to avoid treating other amyloidoses with potentially toxic chemotherapy. Immunofluorescence is the first step to type renal immunoglobulin-derived amyloidosis but the performance characteristics of this method are largely unknown. Here, we establish the sensitivity and specificity of immunofluorescence for diagnosing immunoglobulin-derived amyloidosis in patients whose amyloid typing was performed by the current gold standard of laser microdissection/mass spectrometry. Renal biopsy pathology reports originating from several institutions with a diagnosis of amyloidosis and which had amyloid typing by laser microdissection/mass spectrometry performed at our center were reviewed. Reported immunofluorescence staining for kappa or lambda of 2+ or more, with weak or no staining for the other light chain was considered positive for light chain amyloidosis by immunofluorescence. Based on microdissection/mass spectrometry results, of the 170 cases reviewed, 104 cases were typed as immunoglobulin-derived amyloidosis and 66 were typed as non-immunoglobulin-derived amyloidosis. Immunofluorescence sensitivity for diagnosing immunoglobulin-derived amyloidosis was 84.6%. The remaining 16 cases could not be diagnosed by immunofluorescence due to reported weak staining for all antigens or reported lack of preferential staining for one antigen. Immunofluorescence specificity was 92.4%. Five cases, all amyloid A amyloidosis, were misdiagnosed as immunoglobulin-derived amyloidosis by immunofluorescence. Immunofluorescence failed to accurately differentiate immunoglobulin-derived from non-immunoglobulin-derived amyloidosis in 12.3% of cases of renal amyloidosis. Relying on immunofluorescence alone for determining immunoglobulin-derived vs. non-immunoglobulin-derived amyloidosis may lead to misdiagnosis. Thus, immunofluorescence has inferior sensitivity and specificity compared with laser microdissection/mass spectrometry in the typing of immunoglobulin-derived amyloidosis.

Corticosteroid therapy alone for the treatment of C3 glomerulonephritis in association with monoclonal gammopathy
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INTRODUCTION: C3 glomerulonephritis (C3GN) is a form of proliferative glomerulonephritis characterized by dominant glomerular C3 deposition. There is currently no consensus guideline on therapy for this disease. Experience with corticosteroids alone is scant in C3GN. We report the experience of treating patients with C3GN in association with monoclonal gammopathy with corticosteroid at a single center. MATERIALS AND METHODS: Corticosteroid therapy alone was used to treat 6 patients with C3GN who were also found to have monoclonal gammopathy at the time of presentation. RESULTS: Median age of this cohort was 65 years. Median estimated glomerular filtration rate (eGFR) by MDRD equation was 31.6 mL/min/1.73m2 at presentation. After a median duration of follow-up of 23.5 months, all patients showed improvement in proteinuria: median proteinuria reduced from 2.3 to 0.5 g/d. Four of 6 patients showed improvement in kidney function. One patient who had required renal replacement therapy recovered renal function. Median eGFR at follow-up was 38.7 mL/min/1.73m2. DISCUSSION: In patients with C3GN in association with monoclonal gammopathy, corticosteroid therapy alone may be a viable treatment option. Work-up should be done to exclude a hematologic neoplasm and inherited complement abnormalities before proceeding to corticosteroid therapy.
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Acute Kidney Injury in the Modern Era of Allogeneic Hematopoietic Stem Cell Transplantation.

BACKGROUND AND OBJECTIVES: AKI is a major complication of allogeneic hematopoietic stem cell transplantation, increasing risk of nonrelapse mortality. AKI etiology is often ambiguous due to heterogeneity of conditioning/graft versus host disease regimens. To date, graft versus host disease and calcineurin inhibitor effects on AKI are not well defined. We aimed to describe AKI and assess pre-/post-hematopoietic transplant risk factors in a large recent cohort. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We performed a single-center, retrospective study of 616 allogeneic hematopoietic cell transplant recipients from 2014 to 2017. We defined AKI and CKD based on Kidney Disease Improving Global Outcomes (KDIGO) criteria and estimated GFR using the Chronic Kidney Disease Epidemiology Collaboration equation. We assessed AKI pre-/post-hematopoietic transplant risk factors using cause-specific Cox regression and association of AKI with CKD outcomes using chi-squared test. AKI was treated as a time-dependent variable in relation to nonrelapse mortality. RESULTS: Incidence of AKI by day 100 was 64%. Exposure to tacrolimus and other nephrotoxins conferred a higher risk of AKI, but tacrolimus levels were not associated with severity. Reduced-intensity conditioning carried higher AKI risk compared with myeloablative conditioning. Most stage 3 AKIs were due to ischemic acute tubular necrosis and calcineurin inhibitor nephrotoxicity. KRT was initiated in 21 out of 616 patients (3%); of these 21 patients, nine (43%) recovered and five (24%) survived to hospital discharge. T cell-depleted transplants, higher baseline serum albumin, and non-Hispanic ethnicity were associated with lower risk of AKI. CKD developed in 21% (73 of 345) of patients after 12 months. Nonrelapse mortality was higher in those with AKI (hazard ratio, 2.77; 95% confidence interval, 1.8 to 4.27). CONCLUSIONS: AKI post-hematopoietic cell transplant remains a major concern. Risk of AKI was higher with exposure to calcineurin inhibitors. T cell-depleted hematopoietic cell transplants and higher serum albumin had lower risk of AKI. Of the patients requiring KRT, 43% recovered kidney function. PODCAST: This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_09_07_CJN19801220.mp3.

Serum free light chain level at diagnosis in myeloma cast nephropathy-a multicentre study.

Myeloma cast nephropathy (MCN) is a common cause of severe renal impairment in multiple myeloma (MM). The level of free light chain (FLC) that causes MCN varies substantially and there is uncertainty about the threshold level that should be used to inform clinical practice. In a multicentre cohort study of 103 patients with a diagnosis of MM and biopsy-confirmed MCN made between 2002-2014, we report prospectively measured levels of serum FLC at diagnosis obtained using a single nephelometric assay (Freelite®) and we explore the relationship between serum FLC level at diagnosis with renal outcome and patient survival. Using a landmark approach, overall survival (OS) was compared between patients who achieved independence from dialysis compared to those who remained dialysis dependent at 3-month, 6-month, 9-month, and 12-month time points. The median serum FLC level at diagnosis was 7531 mg/L (range 107-114600). Serum creatinine was 535 µmol/L (range 168-2993) and eGFR 7 ml/min/1.73 m2 (range 1-34). Six patients (5.8%) had an FLC level <1500 mg/L, which is the International Myeloma Working Group threshold for MCN and two patients were below the International Kidney and Monoclonal Gammopathy working group threshold of 500 mg/L; one was hypercalcaemic, and one had high-normal serum calcium level and had received a non-steroidal anti-inflammatory agent. Sixty-nine (67%) patients required haemodialysis treatment of whom 36 (52.1%) recovered independent renal function. Sixty-six (64%) patients died with a median OS of 2.5 years (95% CI 1.8-3.3). A landmark analysis revealed that independence from dialysis was associated with improved survival at 3-months (P = 0.003), 6-months (P = 0.035) and 9-months (P = 0.014); there was no survival benefit observed beyond 12 months (P = 0.146). Serum FLC level at diagnosis was neither associated with renal function recovery nor with OS. This is the largest reported cohort of patients with biopsy-confirmed MCN and prospectively measured serum FLC levels. These results indicate that a serum monoclonal FLC > 500 mg/L should be considered the threshold level associated with the development of MCN.

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.