Myeloma cast nephropathy with diffuse amyloid casts without systemic amyloidosis: two cases report

Background Multiple myeloma (MM) is a plasma-cell derived hematologic malignant disease. The malignant proliferating plasma cells secrete massive monoclonal immunoglobulins which lead to various pathologic types of renal injury. Myeloma cast nephropathy (MCN) is the most common histopathologic lesion with the worst renal prognosis. Rarely, the free light chains in the protein casts can form amyloid fibrils. Here, we reported two rare cases of MCN with diffuse amyloid casts. Case presentation Case 1: A 54-year-old Chinese man presented with a 4-year history of multiple myeloma, proteinuria and hematuria. He had monoclonal IgAλ plus free λ spike in both serum and urine. He had been on chemotherapy for 4 years and maintained normal serum creatinine until 11 months ago. Then, his renal function deteriorated and he went on hemodialysis 4 months before admission. Renal biopsy showed diffuse amyloid casts in the tubular lumens, without any obvious amyloid deposits in other kidney compartments or signs of extra-renal amyloidosis. The amyloid fibrils formed around mononuclear cells which were CD68 negative. According to the morphology and location, these mononuclear cells were considered as tubular epithelial cells. The patient was maintained on chemotherapy and hemodialysis. He died 8 months after renal biopsy. Case 2: A 58-year-old Chinese man presented with a one-and-a-half-year history of proteinuria and slowly rising serum creatinine. He had monoclonal IgDλ spike in both serum and urine. Amyloid casts were observed in the tubular lumens and mononuclear cells could be identified in the center of some casts. There were no amyloid deposits in other kidney compartments and no sign of systemic amyloidosis. The patient also had fine granular deposits along the tubular basement membrane with λ linear staining along tubular basement membrane suggesting light chain deposition disease. He was treated with bortezomib-based chemotherapy followed by lenalidomide-based chemotherapy and achieved very good partial remission (VGPR). After 27 months of follow-up, the patient still showed no signs of systemic amyloidosis. Conclusions These 2 cases of MCN with diffuse amyloid casts have different histopathologic characteristics from the usual myeloma casts and tubular epithelial cells might play important roles in the pathogenesis.

Downregulation of RAB7 and Caveolin-1 increases MMP-2 activity in renal tubular epithelial cells under hypoxic conditions

Tubulointerstitial fibrosis leads to tubular basement membrane thickening and accumulation of interstitial extracellular matrix (ECM). Matrix metallopeptidase-2 (MMP-2) is involved in the breakdown of ECM. Chronic hypoxia often occurs in the kidney tissues of patients with chronic kidney disease. Our previous study reported the effect of autophagy and endocytosis on MMP-2 activity in hypoxia-treated HK-2 cells. In this study, the relationship between the Ras-related protein Rab-7a (RAB7) and MMP-2 activity was further investigated. RAB7 overexpression decreased MMP-2 activity. In contrast, the results for RAB7 knockdown displayed the opposite pattern. Short hairpin RNA technology was used to knockdown Caveolin-1 (Cav-1) or Beclin-1 (Bec-1) in HK-2 cells. The two genes displayed differential effects on MMP-2 activity. Cav-1 and RAB7 interference increased MMP-2 activity. This study suggested that autophagy and endocytosis, RAB7, Cav-1, and Bec-1 may serve as potential mediators for altered MMP-2 activity.

IgG Subclass Expression in Diabetic Nephropathy

Background: This study aimed to analyze the distribution of IgG subclasses in diabetic nephropathy (DN) and its association with clinico-pathological features. Methods: Forty DN cases were analyzed to identify IgG subclasses, as well as collagen IV α5, CD34, and KIM-1.Results: Both IgG and its subclasses showed a linear expression and overlapped with collagen IV α5 on glomerular basement membrane (GBM) and some of tubular basement membrane (TBM), without complement deposition. Eleven cases of IgG subclass deposition along both GBM and TBM were associated with more proteinuria. Five cases of TBM-only IgG subclass deposition were accompanied with less KIM-1 positivity and more arteriosclerosis. The major IgG subclasses expressed on GBM were IgG1 and IgG2, while TBM expression was mainly IgG1 and IgG3. Glomerular IgG1-positive status was associated with less CD34 expression, while IgG2-positive status was associated with thicker GBM. Expression of multiple IgG subclasses along TBM showed less KIM-1 positivity and interstitial inflammation than those with isotype or no IgG subclass expression.Conclusions: IgG subclasses were selectively deposited along GBM and TBM in DN, which was determined by their profiles and severity of glomerular/tubular injury. IgG and its subclass deposition is not causal, but the consequence of renal injury and these positive statuses are associated with different DN injuries.

Idiopathic nodular glomerulosclerosis and differential diagnosis

ABSTRACT Introduction: Idiopathic nodular glomerulosclerosis (ING) is a condition that has a vasculopathic glomerular histological pattern. Case presentation: The authors present the case of a 44-year-old Hispanic smoker female with hypertension and peripheral arterial disease who presented nephrotic syndrome for 2 weeks. The patient was diagnosed with ING by percutaneous renal biopsy results, which showed global nodular mesangial matrix expansion, with linear staining accentuation of glomerular and tubular basement membrane for Immunoglobulin G (IgG) and albumin on immunofluorescence. Conclusions: ING is a rare disease with a poor renal prognosis and wide diagnostic approach; we highlight the importance of analyzing every piece of detail together to reach a definitive diagnosis.

Anti-LRP2 nephropathy with concurrent kidney infiltration by lymphoma

Anti-low-density lipoprotein receptor-related lipoprotein 2 (LRP2) nephropathy/anti-brush border antibody disease is rare and characterized by tubular basement membrane, Bowman’s capsule and glomerular subepithelial immune deposits on kidney biopsy. No reported cases have occurred in patients with lymphoproliferative disorders or monoclonal gammopathies. We present two cases of anti-LRP2 nephropathy that occurred in patients with progressive low-grade B-cell lymphoma and had concurrent kidney infiltration by lymphoma on biopsy. We speculate that underlying immune dysregulation related to lymphoma may contribute to the development of this rare autoimmune kidney disease in some patients.