A 48-year-old woman with progressive proteinuria undergoes renal biopsy. Light microscopy shows a membranoproliferative pattern. Immunofluorescence shows granular polyclonal IgG and C3 in the mesangium and capillary walls. Electron microscopy shows randomly arranged, nonbranching fibrils measuring 16 nm in the mesangium and GBM. Congo red stain is negative. What is the diagnosis?

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

Explanation

Randomly arranged, nonbranching fibrils of 12 to 24 nm that stain with immunoglobulin but are Congo red negative define fibrillary glomerulonephritis, an entity now strongly linked to DNAJB9 as a tissue biomarker. The key discriminator from amyloidosis is Congo red negativity, because amyloid fibrils are thinner (8 to 10 nm) and show apple green birefringence. Immunotactoid glomerulopathy has larger, parallel microtubular arrays (>30 nm) and is strongly associated with lymphoplasmacytic disorders.

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.