A 48-year-old man has proteinuria of 4 g/day and slowly rising creatinine over two years. Renal biopsy shows a lobulated appearance on light microscopy with mild mesangial expansion. Congo red stain is negative. Immunofluorescence shows smudgy IgG and C3 in the mesangium. Electron microscopy reveals randomly arranged, nonbranching fibrils measuring 16 to 24 nm in diameter in the mesangium and glomerular basement membrane. What is the diagnosis?

• A AL amyloidosis
• B Immunotactoid glomerulopathy
• C Cryoglobulinemic glomerulonephritis
• D Fibrillary glomerulonephritis ✓

Explanation

Fibrillary glomerulonephritis is characterized by Congo red negative, randomly arranged fibrils of 16 to 24 nm that deposit in the mesangium and GBM; the associated antigen DNAJB9 is now used diagnostically. Amyloid fibrils are Congo red positive and thinner at 8 to 12 nm. Immunotactoid glomerulopathy shows larger parallel microtubular arrays exceeding 30 nm and is strongly associated with lymphoproliferative disorders and monoclonal gammopathy, which distinguishes it from the polyclonal deposits seen here.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.