Renal-Limited Cryofibrinogen-Associated Glomerulonephritis Diagnosed Using Electron Microscopy.

Cryofibrinogen-associated glomerulonephritis (CryoFiGN) is a rare, diagnostically challenging cause of nephrotic syndrome, and its clinical presentation can vary considerably. Herein, we report the case of a 76-year-old man who presented with nephrotic syndrome; biopsy showed a C3-dominant membranoproliferative pattern of injury. Electron microscopy revealed organised subendothelial microtubular deposits (40-80 nm), confirming CryoFiGN, despite inconclusive results on mass spectrometry. The patient progressed to end-stage kidney disease and later developed systemic vasculitis with skin ulcers and gastrointestinal bleeding. CryoFiGN may initially manifest as a renal-limited disease and evolve into systemic vasculitis. Electron microscopy is pivotal for diagnosis when proteomic analysis is inconclusive and long-term surveillance is warranted.