demonstrated , a specific treatment for MM or lymphoma, such as with bortezomib and rituximab, may also be an effective treatment for PGNMID without an overt malignancy . There is still debate about the desirable strategy of the second biopsy in kidney diseases, especially in lupus nephritis [23C25]. and underwent the second renal biopsy after treatment, showing that chemotherapy was effective for PGNMID clinically and pathologically. Case presentation A 75-year-old man presented with progressive lower leg edema, had nephrotic range proteinuria, hypoalbuminemia, moderate renal failure, and occult blood in his urine. Electrophoresis results showed serum and urinary monoclonal spikes of IgG type immunoglobulin. A renal biopsy specimen showed lobular mesangial proliferation with mesangiolysis, glomerular micro-aneurysm, and endocapillary hypercellularity. Immunofluorescence results revealed strong granular capillary and mesangial staining for IgG1, C3 and light chain in glomeruli without tubular deposits of any immunoglobulin. Electron microscopy also showed dense granular deposits in subendothelial and mesangial areas. PGNMID associated with multiple myeloma (IgG type) was diagnosed on the basis of a subsequent bone marrow examination. Bortezomib and dexamethasone therapy significantly reduced proteinuria and elevated Guaifenesin (Guaiphenesin) serum albumin level. Eight months later, the second renal biopsy showed no active lesions and that the IgG1 and light chain deposits had drastically disappeared. Conclusions This is the first case of PGNMID with multiple myeloma successfully treated with bortezomib and dexamethasone in which comparative renal biopsies were performed before and after treatment. Our findings suggest the pathogenesis of PGNMID and therapeutic options for PGNMID. strong class=”kwd-title” Keywords: Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID), Multiple myeloma, Monoclonal gammopathy Background Nasr et al. recently explained proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) as a novel form of glomerulonephritis that was positive for the deposition of a single IgG subclass and a single light chain isotype in mesangial, subendothelial, or subepithelial regions . On electron microscopy (EM) analysis, these deposits were non-organized, granular, and much Guaifenesin (Guaiphenesin) like those found in monoclonal immunoglobulin deposition disease (MIDD). However, the distribution of glomerular deposits, which mimicked the deposits that occur with regular immune-complex glomerulonephritis, was completely different from that in MIDD . The pathogenesis of PGNMID remains unknown. However, PGNMID recurrence in renal allograft patients suggests that this disease is usually caused by monoclonal immunoglobulin or other pathogenic factors circulating in the serum [3C5]. In 30% of PGNMID cases, there is a monoclonal component in serum . However, PGNMID is usually rarely associated with a hematological malignancy . Including our case, only six cases of PGNMID with multiple myeloma (MM) have been reported [2, 6C8]. In four previous cases, the pathogenic relationship between PGNMID and MM was unclear because a detailed description was not provided [2, 6, 7]. The other case with PGNMID complicated with MM was treated with bortezomib and dexamethasone (BD) therapy and her renal function improved after initiating treatment for MM, though they did not examine second renal biopsy after treatment . Here, we describe a patient with PGNMID associated with MM, for which BD therapy improved PGNMID, comparing two renal biopsies obtained before and after chemotherapy for MM. Case presentation A 75-year-old Japanese man with a history of hypertension, angina pectoris, and colon cancer presented at a local hospital with progressive fatigue. His laboratory test results showed serum albumin of 3.3?g/dL, hemoglobin of 8.0?g/dL, CX3CL1 urine protein of 4+, and negative urinalysis for occult blood. Three months later, he presented with lower leg edema and loss of appetite and was referred to our hospital. He had nephrotic range proteinuria (6.0?g/g), hypoalbuminemia (albumin of 2.8?g/dL), an elevated serum creatinine level (1.1?mg/dL), and urinalysis showed 30-49 red blood cells per high-power field without cellular casts. Decreased levels of serum IgM (14?mg/dL) and IgA (60?mg/dL) compared with a normal IgG level (1202?mg/dL) suggested plasma cell dyscrasia. Protein electrophoresis showed monoclonal spikes (IgG type) in both his serum and urine. A serum cryoglobulin test was negative. An abdominal ultrasound examination showed normal renal size and loss of corticomedullary differentiation in both kidneys. A renal biopsy specimen (Fig.?1A), which contained 24 glomeruli and 4 were sclerotic, showed lobular mesangial proliferation and growth with mesangiolysis, glomerular micro-aneurysm, and endocapillary hypercellularity. The glomerular proliferative changes were global and almost all glomeruli showed similar pattern. Duplication of glomerular basement membrane was also observed. Congo Guaifenesin (Guaiphenesin) reddish staining was unfavorable. Tubulointerstitial scarring involved 30% of the renal cortex. No significant interstitial inflammation was observed. Arteriosclerosis was severe. Open in a separate windows Fig. 1 Renal biopsy histological features of PGNMID associated with multiple myeloma. First renal biopsy (a-k). a Periodic acid-Schiff (PAS) staining: renal histopathology showed lobular glomeruli with mesangial growth and cell proliferation complicated with acute lesions, such as mesangiolysis, 200. b Hematoxylin and eosin (HE) staining: glomerular micro-aneurysm and endocapillary hypercellularity, 400. c Periodic acid methenamine silver (PAM) staining: duplication of glomerular basement membrane (an arrow) and mesangiolysis (an arrow head) was observed, 1000. Congo reddish staining was unfavorable (not shown). d Immunoglobulin G (IgG), e immunoglobulin G1 (IgG1), and f kappa immunostaining were detected.