Immunotactoid Glomerulopathy with Nontuberculous Mycobacterial Infection: A Novel Association

A 70-year-old woman underwent a renal biopsy due to nephrotic syndrome. She had suffered from nontuberculous mycobacterial infection (NTM) for 14 years. The patient was diagnosed as having membranoproliferative glomerulonephritis (MPGN) type 3 and immunoglobulin (Ig)-associated MPGN based upon LM/erythromycin and IF findings, respectively. In high-magnification imaging, electron-dense deposits showed immunotactoid glomerulopathy (ITG). There was no evidence of hematological cancer, and the patient improved after receiving treatments for NTM. To the best of our knowledge, this patient is the first to show an association between ITG and NTM. Although ITG is generally considered as related to lymphoproliferative disease, it is suggested that ITG is driven by bacterial infection and is a potential outcome of Ig-associated MPGN.

A Rare Case of Immunotactoid Glomerulopathy Associated with Hodgkin Lymphoma

Immunotactoid glomerulopathy (ITG) is characterized by Congo red-negative microtubular deposits, and it has been reported as a rare paraneoplastic syndrome due to hematologic malignancies, viral infections, or autoimmune diseases. In hematologic malignancies, multiple myeloma and other mature B-cell malignancies are the most common hematologic malignancies, and Hodgkin lymphoma (HL) is extremely rare. A 59-year-old woman was admitted to our hospital because of a pulmonary mass and proteinuria. Computed tomography-guided lung biopsy confirmed the presence of HL stage IIA. Immunofixation of peripheral blood was positive for immunoglobulin G (IgG) kappa. Renal biopsy showed mesangial proliferation with deposits in the subendothelial lesion and no invasion of the HL. These deposits were positive for IgG3, C3, and kappa light chain but negative for C1q and lambda light chain. Electron microscopy showed randomly aligned tubular structures with a diameter of approximately 50 nm. We diagnosed the patient with immunotactoid nephropathy and HL. After systemic chemotherapy, the patient achieved a complete response and loss of proteinuria. On the contrary, her serum monoclonal gammopathy was observed after chemotherapy. The existence of a monoclonal antibody itself might not be a sufficient factor for ITG in some cases, and an additive trigger is necessary for development.

Monoclonal Gammopathy of Renal Significance: Clinical and Histological Efficacy of a Bortezomib-Based Regimen

Monoclonal Gammopathy of Renal Significance (MGRS) is a group of heterogeneous disorders characterized by renal dysfunction secondary to the production of a monoclonal immunoglobulin by a nonmalignant B cell or plasma cell clone. We report the clinical and histological outcomes of two patients with biopsy-proven MGRS: one patient showed membranoproliferative glomerulonephritis with monoclonal k-light chain and C3 deposits, the second patient showed immunotactoid glomerulopathy. Both patients were treated with a 9-month chemotherapy protocol including bortezomib, cyclophosphamide, and dexamethasone. Renal biospy was repeated after 1 year. The estimated glomerular filtration rate (eGFR) increased from 22.5 (baseline) to 40 ml/min per 1.73 m2 after 12 months, then to 51.5 ml/min per 1.73 m2 after 24 months; proteinuria decreased from 4.85 (baseline) to 0.17 g/day after 12 months, then to 0.14 g/day after 24 months. Repeat renal biopsies showed a dramatic improvement of the glomerular proliferative lesions and near complete disappearance of the immune deposits. A bortezomib-based treatment proved very effective and was well-tolerated in the two patients presenting with clinically and histologically aggressive MGRS.

Fibrilo-Tactoid Glomerulonephritis: A Possible Novel Morphological Variant

Fibrillary and immunotactoid glomerulonephritis are infrequent causes of primary nephrotic range proteinuria and are poorly understood. Recent significant developments include the discovery of DNA JB9 antigen in fibrillary glomerulonephritis. Here, we present a case of a middle-aged woman who presented with nephrotic range proteinuria, hematuria, and normal renal function. Renal biopsy revealed fibrils that were randomly arranged on electron microscopy. They were of small size and congo red negative similar to the ones found in fibrillary glomerulonephritis, but were also DNA JB 9 negative, and had a hollow core like in immunotactoid glomerulopathy. Though we try to classify these conditions into either immunotactoid glomerulonephropathy (ITGN) or fibrillary glomerulonephritis (FGN), there are scenarios such as this case where it does not fit into either and is probably an overlap or intermediate variant of these two conditions. Pathological features of these glomerulonephrites are discussed together with their clinical implications, treatment choices, and diagnostic importance.