A 68-year-old man with a 10-year history of rheumatoid arthritis develops proteinuria (4 g/day), hepatomegaly, and renal insufficiency. Rectal biopsy shows Congo red positive material with apple-green birefringence under polarized light. Which specific amyloid fibril protein is responsible in this secondary systemic amyloidosis?
- A AL amyloid (immunoglobulin light chains)
- B AA amyloid (serum amyloid A-derived protein) ✓
- C ATTR amyloid (transthyretin)
- D Aβ2M amyloid (β2-microglobulin)
Explanation
Secondary (reactive systemic) amyloidosis (AA amyloidosis) occurs in the setting of chronic inflammatory conditions (RA, ankylosing spondylitis, IBD, recurrent infections). Serum amyloid A (SAA), an acute-phase reactant, is chronically elevated and undergoes proteolytic conversion to amyloid A (AA) fibrils. AA amyloid deposits preferentially in kidneys (nephrotic syndrome), liver, and spleen. AL amyloid (light chain) is associated with plasma cell dyscrasias (myeloma). ATTR (transthyretin) causes cardiomyopathy in elderly (wild-type) or hereditary ATTR. Aβ2M is seen 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.