A 35-year-old woman with rheumatoid arthritis develops proteinuria. Renal biopsy shows apple-green birefringence on Congo red under polarized light. The deposited protein subunit is most likely:
- A AL amyloid (immunoglobulin light chains) from plasma cells
- B ATTR amyloid (transthyretin) from aging
- C AA amyloid (serum amyloid A-derived) from chronic inflammation ✓
- D Abeta2M amyloid (beta2-microglobulin) from dialysis
Correct answer: C. AA amyloid (serum amyloid A-derived) from chronic inflammation
Explanation
AA (secondary) amyloidosis complicates chronic inflammatory diseases including rheumatoid arthritis. The precursor protein is serum amyloid A (SAA), an acute-phase reactant; after proteolytic cleavage, AA fibrils deposit in kidney, spleen, and liver. AL amyloidosis complicates plasma cell dyscrasias; ATTR amyloid is age-related or familial; Abeta2M occurs in long-term dialysis patients.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.