A 45-year-old woman with rheumatoid arthritis undergoes fat pad biopsy showing amyloid deposits that stain with Congo red and show apple-green birefringence under polarized light. Mass spectrometry of the deposits identifies SAA-derived peptides. What is the correct amyloid type, precursor protein, and associated clinical context in this scenario?

• A AL amyloid; precursor is immunoglobulin light chain kappa or lambda; most commonly associated with plasma cell dyscrasias; deposits preferentially in the heart causing restrictive cardiomyopathy
• B ATTR amyloid; precursor is transthyretin (TTR); seen in familial and senile systemic amyloidosis; deposits primarily in the heart and peripheral nerves
• C Aβ2M amyloid; precursor is beta-2 microglobulin; seen in long-term dialysis patients; deposits in periarticular and carpal tunnel regions
• D AA amyloid; precursor is serum amyloid A (SAA), an acute-phase reactant overproduced in chronic inflammation; deposits preferentially in spleen, liver, and kidney; the fibrils are composed of the N-terminal fragment of SAA after protease cleavage ✓

Explanation

This is secondary (AA) amyloidosis, associated with chronic inflammatory conditions such as rheumatoid arthritis, ankylosing spondylitis, chronic infections, and periodic fever syndromes. SAA is an apolipoprotein synthesized massively by the liver as an acute-phase reactant, driven by IL-1, IL-6, and TNF. The N-terminal 76 amino acid fragment of SAA forms the amyloid AA fibrils. Kidneys (proteinuria, nephrotic syndrome), spleen (splenomegaly), and liver (hepatomegaly) are the primary organs affected. Congo red with apple-green birefringence confirms amyloid; immunohistochemistry or mass spectrometry identifies the fibril type.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.