MONOCLONAL IMMUNOGLOBULIN G1-KAPPA FIBRILLARY GLOMERULONEPHRITIS

We report here a case of fibrillary glomerulonephritis arising in a 43 -year-old man with a polyclonal gammopathy, who presented with progres sive renal insufficiency, microscopic hematuria, and mild proteinuria (0.7 g/d). Ultrastructural studies showed deposits of randomly oriente d fibrils in the glomerular mesangium and adjacent portions of some gl omerular basement membranes, with a mean fibril thickness of 14.3 nm, highly consistent with fibrillary glomerulonephritis. The Congo red st ain was negative on histologic sections, Immunofluorescence studies re vealed strong mesangial and focal glomerular capillary staining for im munoglobulin Og) G, complement (C) 3, and kappa light chains, with min imal staining for IgA, IgM, C1q, or lambda light chains. The IgG prese nt was entirely of the IgG1 subclass. This case is quite unusual for f ibrillary glomerulonephritis, which typically presents with polyclonal IgG deposits and IgG4 as the dominant IgG subclass present. Monoclona l deposits are more frequently associated with immunotactoid glomerulo pathy, characterized ultrastructurally by microtubule-like structures 30 to 50 nn thick, often in parallel arrays. The present case illustra tes that although fibrillary glomerulonephritis and immunotactoid glom erulopathy might be distinguishable on ultrastructural grounds, there is overlap between these two entities with respect to the potential co mposition of the glomerular deposits present.