Question

A patient with long-standing rheumatoid arthritis develops nephrotic-range proteinuria. Renal biopsy with Congo red stain shows apple-green birefringence under polarised light. Which type of amyloid protein is most likely deposited?

• A. AA (serum amyloid A-derived) amyloid
• B. AL (immunoglobulin light chain) amyloid
• C. Abeta₂-microglobulin amyloid
• D. ATTR (transthyretin) amyloid

Hint:

Acute-phase reactant SAA is the precursor in reactive amyloidosis.

Answer 1

The Correct Option is A

Step 1: Identify the clinical setting. The amyloidosis here is secondary (reactive) to a chronic inflammatory disease - rheumatoid arthritis. Other classic causes are chronic infections (TB, osteomyelitis, bronchiectasis), IBD and familial Mediterranean fever.

Step 2: Link inflammation to the precursor protein. In chronic inflammation the liver produces serum amyloid A (SAA) as an acute-phase reactant. Persistent elevation leads to its proteolytic processing and deposition as AA amyloid.

Step 3: Select the answer. Chronic inflammation to AA amyloidosis (secondary/reactive systemic amyloidosis), which characteristically affects the kidneys.

Step 4: Why the others are wrong - AL amyloid derives from immunoglobulin light chains and is seen in plasma cell dyscrasias/multiple myeloma (primary amyloidosis); Abeta₂-microglobulin accumulates in patients on long-term haemodialysis; ATTR is from transthyretin (senile cardiac or hereditary amyloidosis).

Key fact: Chronic inflammation produces SAA to AA amyloid (secondary amyloidosis).