A 55-year-old man with rheumatoid arthritis develops progressively enlarging kidneys with proteinuria. Renal biopsy stained with Congo red under polarized light shows apple-green birefringence in the glomeruli and arterioles. Immunohistochemistry confirms SAA protein deposits. This form of amyloidosis is classified as:
- A AL amyloidosis (primary), from immunoglobulin light chains
- B ATTR amyloidosis (senile/hereditary), from transthyretin
- C Aβ2M amyloidosis, from beta-2 microglobulin in dialysis patients
- D AA amyloidosis (secondary), from serum amyloid A protein ✓
Explanation
AA amyloidosis is the form associated with chronic inflammatory conditions including rheumatoid arthritis, inflammatory bowel disease, osteomyelitis, and familial Mediterranean fever. The precursor protein is serum amyloid A (SAA), an acute-phase reactant produced by the liver. Sustained chronic inflammation drives persistently elevated SAA levels, leading to proteolytic cleavage and fibrillogenesis. Kidney (proteinuria/nephrotic syndrome), spleen, and liver are predominantly affected. AL amyloidosis is associated with plasma cell dyscrasias; ATTR amyloidosis preferentially affects the heart and peripheral nerves.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.