Congophilic fibrillary glomerulonephritis recurrence post-renal transplant: diagnostic challenges and proteomic insights.

Fibrillary glomerulonephritis (FGN) is a rare kidney disease characterized by the deposition of Congo red (CR) negative fibrils measuring 12 to 24 nm in diameter on electron microscopy. Recently, DnaJ heat shock protein family (Hsp40) member B9 (DNAJB9) detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was discovered to be a sensitive and specific biomarker for FGN. This report presents the first documented case of recurrent congophilic FGN, a rare glomerular disease with features resembling amyloidosis, occurring two years and eight months after a renal transplant. Diagnosis of both primary and recurrent FGN was confirmed through DNAJB9 detection using advanced laser microdissection and LC-MS/MS techniques. The recurrent FGN exhibited features consistent with amyloidosis, including CR positivity, characteristic microscopic findings, and fibrils on electron microscopy with a 9 to 15 nm diameter. This case demonstrates that FGN could recur in the transplanted kidney as congophilic GN with characteristic findings of amyloidosis, and it is difficult, if not impossible, to render a correct diagnosis without LC-MS/MS or immunohistochemistry.