A 45-year-old man with chronic discharging osteomyelitis of the femur for two years develops progressive edema and proteinuria of 5 g/day. Renal biopsy shows amorphous eosinophilic material in the glomeruli and vessel walls that stains salmon pink with Congo red and gives apple-green birefringence under polarized light. The deposited protein is most likely:

• A Serum amyloid A protein ✓
• B Beta-2 microglobulin
• C Lambda light chain variable region fragments
• D Transthyretin

Explanation

Chronic suppurative inflammation drives sustained hepatic production of serum amyloid C, which is deposited as AA amyloid in kidneys, liver and spleen. AL amyloid (option C) arises from plasma cell dyscrasias producing monoclonal light chains, beta-2 microglobulin amyloid complicates long-term dialysis, and transthyretin causes familial and senile systemic forms unrelated to chronic osteomyelitis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.