A 52-year-old man with proteinuria undergoes renal biopsy. Electron microscopy shows randomly arranged, nonbranching fibrils measuring 16 nm within the mesangium and GBM. Congo red stain is negative. Immunofluorescence is positive for IgG, C3, and DNAJB9. What is the diagnosis?

• A AL amyloidosis
• B Immunotactoid glomerulopathy
• C Fibrillary glomerulonephritis ✓
• D Light chain deposition disease

Explanation

Fibrillary glomerulonephritis shows random nonbranching fibrils of 12 to 24 nm that are Congo red negative, distinguishing it from amyloid, whose fibrils are 7 to 10 nm and Congo red positive. DNAJB9 is a sensitive marker for fibrillary GN. Immunotactoid glomerulopathy shows larger microtubular structures over 30 nm arranged in parallel bundles, usually with monoclonal immunoglobulin, which excludes option B.

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.