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BACKGROUND: Monoclonal immunoglobulin deposition disease (MIDD) is characterized by the non-amyloid deposition of monoclonal immunoglobulin fragments in the basement membranes. Heavy chain deposition disease (HCDD) is a type of MIDD. HCDD is an extremely rare disease, and only three cases have been reported in Japan up to the present. The prognosis of HCDD is very poor, and optimal treatment has not been established. Only a few cases of HCDD with favorable long-term renal prognosis have been reported to date. CASE PRESENTATION: The authors describe a 61-year-old woman who presented with massive proteinuria, progressive kidney impairment, and hypocomplementemia. Kidney biopsy was performed for a precise diagnosis. On light microscopy, glomerules were lobulated and presented with nodular sclerosing glomerulopathy with membranoproliferative glomerulonephritis-like features. Immunofluorescence studies were positive for IgG, C3, and C1q within the mesangial nodules and in a linear distribution along the capillary walls without associated deposition of light chains. Staining for IgG showed the presence of linear deposits along tubular basement membranes. The analysis of the IgG subclass stain demonstrated intense positivity for IgG3 only. Electron microscopy revealed non-organized electron-dense deposits in the expanded mesangial area and inner aspect of the glomerular basement membranes. In accordance with the histological findings, we diagnosed γ3-HCDD. There was no evidence of plasma cell dyscrasia as a result of bone marrow aspiration. Serum and urine monoclonal proteins were not detected by immunoelectrophoresis and immunofixation electrophoresis. The serum free light chain ratio was within normal range. At first, prednisolone was administrated at a dose of 40 mg/day. However, a therapeutic effect was not observed. Urinary protein was not decreased and renal function further deteriorated. Therefore, melphalan plus prednisolone (MP) therapy was initiated. After 4 courses of MP therapy, the clinical parameters, including proteinuria, serum creatinine, albumin, and complement level (C3 and C4) were ameliorated. To date, the patient has been followed for 28 months, and long-term renal survival has been observed. CONCLUSIONS: In this case, hematologic disease such as multiple myeloma was not detected; however, MP therapy was effective. Recently, the novel concept of monoclonal gammopathy of renal significance (MGRS) has been reported. MIDD, which includes HCDD, is one category of MGRS. In MGRS, aggressive chemotherapy may induce favorable renal outcomes.

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A 73-year-old woman was diagnosed with pulmonary Mycobacterium avium complex (MAC) infection and received no treatment. Disease progression was evident one year later with the development of myeloperoxidase-antineutrophil cytoplasmic antibody (ANCA) titers and systemic symptoms of a fever, polyarthritis, purpura, and rapidly progressive glomerulonephritis. Her symptoms did not improve with antibiotic treatment. A renal biopsy revealed crescentic glomerulonephritis with immunodeposition. According to these findings, she was diagnosed with ANCA-associated vasculitis (AAV) superimposed on infection-related glomerulonephritis (IRGN). Although there was a risk of aggravating an underlying infection, the combination therapy of corticosteroid and antibiotics improved AAV, IRGN, and even the lung radiological findings. To the best of our knowledge, this is the first case of AAV and IRGN secondary to pulmonary MAC infection.

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The term cryoglobulinemia (CG) is used to refer to vasculitis due to so-called mixed cryoglobulins containing immune complexes. Although most cases of monoclonal CG, called type I CG, are asymptomatic, purpura, skin ulcers, and renal failure develop in some cases. Hematological disorders are the underlying diseases in most cases, on which the therapeutic strategies available and the prognosis of patients depends. We here report a case of a 47-year-old man who had pain in both his ankles, with palpable purpura and epistaxis, and presented with acute renal failure. Monoclonal immunoglobulin (Ig) G-κ protein was detected and cryoglobulin was also positive. Renal biopsy revealed emboli with a fibrillar structure in the glomeruli and renal tubule lumina. The complication of thrombotic microangiopathy (TMA) occurred during the course. Therefore, plasma exchange and hemodialysis were added to methylprednisolone pulse therapy. The treatment was successful, dissipating the purpura. However, the purpura relapsed and renal dysfunction progressed when the administration of oral steroids was tapered. Bone marrow biopsy was performed again, which indicated an increase in abnormal plasma cells. The patient was finally diagnosed as multiple myeloma. Then, bortezomib-dexamethasone therapy was initiated. This is the first case of type I CG with monoclonal IgG complicated by TMA during the course; it provides insight into the pathogenesis of renal dysfunction associated with type I CG.