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Abstract: SA-PO1086

Congo Red Positive Fibrillary Glomerulonephritis

Session Information

Category: Pathology and Lab Medicine

  • 1502 Pathology and Lab Medicine: Clinical

Authors

  • Riazy, Maziar, University of Washington, Seattle, Washington, United States
  • Andeen, Nicole K., Oregon Health & Science University, Portland, Oregon, United States
  • Alpers, Charles E., University of Washington Medical Center, Seattle, Washington, United States
  • Smith, Kelly D., University of Washington, Seattle, Washington, United States

Group or Team Name

  • UW renal Pathology
Background

Fibrillary glomerulonephritis (FGN) is characterized by the glomerular deposition of Congo red-negative fibrillary material with fibers that are larger in diameter than amyloid fibrils . With recent identification of DnaJ homolog subfamily B member 9 (DNAJB9) as a sensitive and specific marker for FGN, we sought to examine the specificity of these traditional diagnostic criteria used to distinguish FGN and amyloidosis.

Methods

The study population consisted of renal biopsies accessioned at the University of Washington, Seattle, USA from 01/01/2014 to 05/15/2018. We performed a database search of pathology reports for terms “fibrillary” and “atypical amyloid”. Cases were included if all of the following: 1) glomerular and/or extra glomerular fibrillary deposits were present 2) Congo red stain was performed 3) FGN was diagnosed by conventional criteria and/or DNAJB9 was demonstrated in the deposits by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and/or immunofluorescence.

Results

During the study period, 49 patients were diagnosed with FGN, of which 4 patients’ biopsies had positive Congo red staining. The most prominent light microscopic findings were necrotizing and crescentic lesions (2 cases) and mesangial expansion with glomerular basement membrane thickening (2 cases). Immunofluorescence showed polytypic IgG staining in all 4 cases. The average fibrillary diameter ranged from 8.8-14.2 nm with two cases below the 12 nm diagnostic cut-off (figure).

Conclusion

Congo red positive staining and fibril diameter less than 12 nm should not be used as exclusion criteria for the diagnosis of FGN. The diagnosis of FGN should be considered in Congo red positive biopsies with findings that are atypical or inconclusive for amyloidosis, and LC-MS/MS and/or DNAJB9 immunostaining should be performed to confirm or exclude the diagnosis of FGN.

The Congo red and immunofluorescence (light chains and DNAJB9) staining and the fibrillary organization of the deposits in one of the cases. LC-MS/MS of the Congo red positive glomerular deposits showed DNAJB9 but no amyloidogenic peptides.

Funding

  • Clinical Revenue Support