A 55-year-old woman has nephrotic-range proteinuria and mild renal impairment. Biopsy shows a lobulated glomerulus with mesangial and capillary wall expansion by randomly arranged fibrils measuring 12 to 18 nm on electron microscopy. Congo red stain is negative. Immunofluorescence shows smudgy polyclonal IgG and C3. Which diagnosis fits these findings?

• A AA amyloidosis
• B Diabetic nodular glomerulosclerosis
• C Immunotactoid glomerulopathy
• D Fibrillary glomerulonephritis ✓

Explanation

Fibrillary glomerulonephritis features random 12 to 18 nm fibrils in the mesangium and capillary walls, polyclonal smudgy IgG and C3 staining, Congo red negativity, and recent linkage to DNAJB9 as a tissue biomarker. Amyloid fibrils are thinner at 8 to 10 nm and Congo red positive, eliminating option A. Immunotactoid glomerulopathy shows larger parallel microtubular arrays over 30 nm, usually monoclonal, and is associated with lymphoproliferative disease. Diabetic nodules contain no fibrils.

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.