When noncongophilic glomerular fibrils do not represent fibrillary glomerulonephritis: nonspecific mesangial fibrils in sclerosing glomeruli.

In addition to fibrillary glomerulonephritis (FGN), Congo red negative mesangial fibrils may commonly be seen in sclerosing glomerular diseases. Rarely, these nonspecific mesangial fibrils (NMF) may mimic fibrils in FGN and cause a differential diagnostic pitfall. Following an interesting case of sclerosing crescentic glomerulonephritis with abundant NMF (which is presented in some detail) we have reviewed our renal biopsy files for a period of two and a half years and found additional 16 cases where the presence of NMF warranted studies to exclude FGN and other diseases with fibrillary deposits. The immunofluorescence pattern characteristically seen in FGN was not present in any of these cases. Our data confirm that mesangial fibrillary material seen ultrastructurally in sclerosing glomeruli with negative or nonspecific immunofluorescence (IF) represents a nonspecific reaction of the mesangial matrix to chronic glomerular injury. The presence of NMF should not lead to the erroneous diagnosis of FGN. Negative or nonspecific immunofluoresence, localization to the mesangium in a usually segmental fashion, and the more bundle-like than random arrangement of fibrils are helpful diagnostic hints in differentiating NMF from fibrils in FGN.