Dual Occurrence of DNAJB-9 Positive Fibrillary Glomerulonephritis and Diffuse Lupus Nephritis: A Unique Overlap Glomerulopathy

Cases of lupus nephritis (LN) with substructured deposits detected by electron microscopy are not uncommon in nephropathology practice. Rare cases of LN have been reported to show fibril formation similar to the type found in fibrillary glomerulonephritis (FGN). It is uncertain if fibril formation in such cases represents a unique manifestation of LN or LN with a superimposed FGN. FGN is a rare disease with unknown pathogenesis and a poor prognosis. Diagnosis of FGN has required the demonstration, by electron microscopy, of haphazardly arranged fibrils measuring 10 to 30 nm in thickness in the mesangium or along the glomerular basement membranes. DnaJ homolog subfamily B member 9 (DNAJB-9) immunohistochemical staining is a recently discovered sensitive and specific marker for FGN and is now considered essentially pathognomonic for FGN. No cases of bone fide LN with concurrent DNJAB-9 positive FGN have been reported. Here, we report on one such overlap glomerulopathy showing well developed features of LN (full house immunofluorescence staining, strong C1q staining, extraglomerular deposits, tubuloreticular inclusions) with concurrent fibrillar deposits with strong DNAJB-9 positivity highly consistent with FGN.