A 45-year-old woman with long-standing rheumatoid arthritis develops progressive nephropathy. Renal biopsy shows Congo red-positive deposits in the mesangium and vessel walls that show apple-green birefringence under polarized light. The amyloid protein most likely responsible is:

• A AL amyloid (immunoglobulin light chains)
• B ATTR amyloid (transthyretin)
• C Aβ2M amyloid (beta-2 microglobulin)
• D AA amyloid (serum amyloid A protein) ✓

Explanation

Secondary (reactive) amyloidosis in chronic inflammatory conditions (RA, chronic osteomyelitis, bronchiectasis, inflammatory bowel disease, familial Mediterranean fever) deposits AA amyloid, derived from serum amyloid A (SAA), an acute-phase reactant produced by the liver. AA amyloid preferentially deposits in kidneys, spleen, and liver. AL amyloid is deposited in primary amyloidosis or myeloma-associated amyloidosis; ATTR amyloid causes hereditary and senile cardiac amyloidosis; Aβ2M is associated with long-term dialysis.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.