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Fibrillary glomerulonephritis is a rare disease affecting less than 1% of all native kidney biopsies and is due to fibrillary deposits of immunoglobulin that by electron microscopy are randomly arranged fibrils of approximately 18-20 nm in diameter. Clinically patients will present with proteinuria and hematuria. Histologically it can show several patterns within glomeruli including mesangial proliferative, membranoproliferative, or even a crescentic pattern of glomerular injury. Positive staining with the DNAJB9 stain is extremely useful in identifying this disease as it is around 98% sensitive and 99% specific for Fibrillary GN. Associations with Fibrillary GN include autoimmune disease, infection (i.e. Hepatitis C), dysproteinemias, and malignancy. Finally, rare cases of Fibrillary GN can be immunoglobulin negative by routine and paraffin (with pronase digestion) immunofluorescence (See reference).
Said S, et al. Immunoglobulin-Negative DNAJB9-Associated Fibrillary Glomerulonephritis: A Report of 9 Cases. AJKD 2020 Advance online publication. https://doi.org/10.1053/j.ajkd.2020.04.015.