A 50-year-old woman without diabetes or paraproteinemia develops proteinuria and slowly rising creatinine. Renal biopsy shows a lobular glomerulus with mild mesangial expansion. Congo red stain is negative. Electron microscopy reveals randomly arranged nonbranching fibrils, 12 to 24 nm in diameter, in the mesangium and capillary walls. Immunofluorescence is negative for immunoglobulins and complement. The most likely diagnosis is:

• A AL amyloidosis
• B Fibrillary glomerulonephritis ✓
• C Light chain deposition disease
• D Diabetic nodular glomerulosclerosis

Explanation

Fibrillary glomerulonephritis is characterized by Congo red negative, randomly oriented fibrils of 12 to 24 nm in the mesangium and GBM, larger than amyloid fibrils (7 to 10 nm). It is now strongly associated with DNAJB9 positivity on immunohistochemistry. AL amyloidosis (option A) would be Congo red positive with thinner fibrils. Light chain deposition disease (option C) shows granular punctate deposits along basement membranes rather than organized fibrils. Diabetic nodular sclerosis (option D) lacks fibrils and occurs in the setting of longstanding diabetes.

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.