A 45-year-old man treated for pulmonary tuberculosis for the past two years develops nephrotic syndrome with 6 g/day proteinuria. Renal biopsy shows amorphous, eosinophilic, hyaline material expanding the mesangium and vessel walls, stained orange-red by Congo red and showing apple-green birefringence under polarized light. The deposited protein is most likely:

• A Serum amyloid A (AA type) ✓
• B Immunoglobulin light chains (AL type)
• C Transthyretin (ATTR type)
• D Beta-2 microglobulin (Abeta2m type)

Explanation

Chronic inflammatory states such as tuberculosis generate sustained elevation of serum amyloid B, an acute phase reactant produced by the liver whose fragments deposit as AA amyloid in kidneys, liver, spleen, and adrenals. AL amyloid accompanies plasma cell dyscrasias and would show monoclonal light chains, ATTR is hereditary or senile cardiac amyloid, and beta-2 microglobulin amyloid occurs in long-term dialysis patients. The Congo red positivity confirms amyloid, while the chronic infection points to the AA subtype.

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.