Immune-complex-mediated membranoproliferative glomerulonephritis with linear IgG staining resembling atypical anti-glomerular basement membrane disease: a case report.

Anti-glomerular basement membrane (anti-GBM) disease typically presents as rapidly progressive glomerulonephritis, however an atypical anti-GBM nephritis with various light microscopic findings without crescentic formation has been reported in recent years. The findings reported including cases with membranoproliferative glomerulonephritis (MPGN) pattern. Few reports have been able to follow the course of the disease over a long period of time. We report a case of MPGN associated with the spectrum of atypical anti-GBM nephritis that showed a slowly progressive course over more than eight years. A 49-year-old man underwent kidney biopsy because of hypertension, proteinuria, and mild renal insufficiency. The findings on kidney biopsy showed the findings of MPGN. Immunofluorescence microscopy revealed bright linear staining of IgG on the GBM. Electron microscopy showed subepithelial, intra-basement membrane, subendothelial, and paramesangial electron-dense deposits. Serum anti-GBM antibodies were negative. Proteinuria had been present for 4 years prior to the renal biopsy, however no worsening of renal function was observed. Because of worsening proteinuria and the presence of endocapillary hypercellularity in the tissues, the intravenous and oral steroids were started. Although the proteinuria showed slight improvement, the serum creatinine level was stable around 1.5-1.7 mg/dl. Although some indolent cases of atypical anti-GBM syndrome were reported previously, compared with these cases, our patient had more stable renal function for a long time. This is a rare case of resembling atypical anti-GBM disease that shows MPGN with linear IgG staining having a long-term indolent course and without secondary etiology.