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

A 76-year-old man presented with nephrotic syndrome caused by cryofibrinogen-associated glomerulonephritis (CryoFiGN), a rare and diagnostically challenging condition.

• The patient was 76 years old at presentation.
• Clinical presentation was nephrotic syndrome.
• CryoFiGN is described as a rare cause of nephrotic syndrome with considerable variation in clinical presentation.

Renal biopsy demonstrated a C3-dominant membranoproliferative pattern of injury.

• Biopsy findings showed a C3-dominant membranoproliferative pattern.
• The biopsy pattern was consistent with membranoproliferative glomerulonephritis (MPGN).
• The C3-dominant pattern was identified on immunofluorescence or immunohistochemistry as part of the diagnostic workup.

Electron microscopy revealed organised subendothelial microtubular deposits measuring 40–80 nm, confirming the diagnosis of CryoFiGN.

• Deposits were described as 'organised subendothelial microtubular deposits.'
• Microtubular deposit diameter ranged from 40 to 80 nm.
• Electron microscopy confirmed the diagnosis of CryoFiGN despite inconclusive results on mass spectrometry.
• Mass spectrometry (proteomic analysis) was inconclusive in this case.

The patient progressed to end-stage kidney disease and subsequently developed systemic vasculitis with skin ulcers and gastrointestinal bleeding.

• Disease progression included development of end-stage kidney disease.
• Systemic vasculitis manifested after the initial renal-limited presentation.
• Systemic involvement included skin ulcers and gastrointestinal bleeding.
• This case illustrates that CryoFiGN may initially manifest as renal-limited disease before evolving into systemic vasculitis.

Electron microscopy is pivotal for diagnosing CryoFiGN when proteomic analysis is inconclusive, and long-term surveillance is warranted.

• Mass spectrometry yielded inconclusive results in this case, highlighting its diagnostic limitations.
• Electron microscopy provided the definitive diagnostic information by identifying the characteristic microtubular deposits.
• The authors recommend long-term surveillance given the potential for disease evolution from renal-limited to systemic disease.
• CryoFiGN can evolve into systemic vasculitis, underscoring the importance of ongoing follow-up.