An atypical case of proliferative glomerulonephritis with monoclonal Immunoglobulin G1 κ deposits with organized structural deposits.

A 67-year-old man with a history of pancreatic cancer, diagnosed 2 years ago was referred to the hospital with proteinuria and renal dysfunction. His medical history included hypertension. A renal biopsy was performed to investigate renal damage. Light microscopy revealed membranoproliferative glomerulonephritis without Congo red stain positive deposits. Immunofluorescence findings showed positive staining of immunoglobulin G (IgG), fibrinogen and κ-light chain, but not λ-light chain. Additionally, the IgG subclass showed only IgG1 positive staining. Electron microscopy revealed electron-dense deposits in the mesangial and paramesangial regions. They were arranged in microfiber structures; approximately 30 nm in diameter, in a parallel fixed direction alignment. Notably, a characteristic ladder-like formation was observed within them. Glomerular diseases caused by nonamyloid fibrillar deposits are diagnosed based on the clinicopathological features.　Moreover, mass spectrometry confirmed the presence of monoclonal IgG1κ in the glomeruli. As a result, this disease was diagnosed as an atypical proliferative glomerulonephritis with monoclonal IgG1κ deposits (PGNMID). Here, we report an atypical case of PGNMID characterized by a unique ladder-like formation containing fibrinogen and fibronectin in organized structures.