A 65-year-old man with a 25-year history of poorly controlled seropositive rheumatoid arthritis presents with progressive abdominal distension, bilateral pitting pedal edema, and macroglossia. Urine protein is 4.2 g/day. Serum albumin is 2.1 g/dL. Congo red staining of a fat pad biopsy shows apple-green birefringence under polarized light. Which type of amyloid protein is most likely deposited?
- A AL (light chain) amyloid
- B AA (serum amyloid A) amyloid ✓
- C ATTR amyloid
- D Beta-2 microglobulin amyloid
Correct answer: B. AA (serum amyloid A) amyloid
Explanation
Long-standing chronic inflammatory conditions such as rheumatoid arthritis lead to sustained elevation of the acute-phase reactant serum amyloid A (SAA), which is cleaved and deposited as AA amyloid. This causes secondary (reactive) amyloidosis manifesting as nephrotic syndrome and organomegaly. AL amyloid is associated with plasma cell dyscrasias, ATTR with familial or senile transthyretin disease, and beta-2 microglobulin with long-term hemodialysis.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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