A 68-year-old man has nephrotic-range proteinuria and a serum monoclonal M spike on electrophoresis. Renal biopsy shows amorphous, eosinophilic material expanding the mesangium and capillary walls. This material stains orange-red with Congo red and shows apple-green birefringence under polarized light. Electron microscopy shows randomly oriented, nonbranching fibrils about 8 to 12 nm thick. What type of amyloid is most likely present?
- A AL amyloid derived from immunoglobulin light chains ✓
- B AA amyloid derived from serum amyloid A
- C ATTR amyloid derived from transthyretin
- D Abeta2M amyloid derived from beta-2 microglobulin
Correct answer: A. AL amyloid derived from immunoglobulin light chains
Explanation
Renal amyloidosis in an adult with a monoclonal M spike is almost always AL type, produced by monoclonal plasma cells secreting light chains that form amyloid fibrils. AA amyloid occurs after chronic inflammatory states such as tuberculosis, bronchiectasis or familial Mediterranean fever and lacks an M spike. ATTR is seen in senile cardiac and familial forms, and Abeta2M amyloid complicates long-term dialysis, typically affecting joints rather than causing nephrotic syndrome.
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.