Renal biopsy from a 60-year-old man with nephrotic syndrome shows mesangial expansion and mild proliferation on light microscopy. Immunofluorescence reveals IgG and C3 in a granular pattern. Electron microscopy demonstrates randomly arranged, nonbranching fibrils measuring 16 to 20 nm in diameter within the mesangium and glomerular basement membranes. Congo red stain is negative. The most likely diagnosis is:

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

Explanation

Fibrillary glomerulonephritis shows randomly oriented fibrils of 12 to 24 nm that resemble amyloid ultrastructurally but are Congo red negative and contain polyclonal IgG and A3; DNAJB9 is the marker antigen. Amyloid fibrils are thinner, 7 to 10 nm, and Congo red positive. Immunotactoid glomerulopathy shows larger parallel microtubular arrays exceeding 30 nm, usually with monoclonal immunoglobulin. Light chain deposition disease produces powdery granular deposits along tubular and glomerular basement membranes, not 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.