A 62-year-old man presents with macroglossia, periorbital purpura, and nephrotic-range proteinuria. Serum free light chains show a kappa level of 320 mg/L with a kappa/lambda ratio of 14. A fat pad biopsy shows amorphous eosinophilic extracellular deposits. Which staining finding confirms the diagnosis?
- A Strong nuclear cyclin D1 expression in the deposit-bearing tissue
- B Apple-green birefringence of Congo red-stained deposits under polarized light ✓
- C Reticulin staining showing dense fibrosis replacing the parenchyma
- D Periodic acid-Schiff positivity with diastase resistance of the deposits
Correct answer: B. Apple-green birefringence of Congo red-stained deposits under polarized light
Explanation
Amyloid deposits stained with Congo red show apple-green birefringence under polarized light, the definitive histological proof of amyloidosis regardless of type; typing as AL follows with serum free light chains and immunohistochemistry for light chains. Macroglossia, periorbital purpura, and nephrotic proteinuria are classic AL manifestations from a clonal plasma cell disorder. Cyclin D1 relates to mantle cell lymphoma, and PAS diastase resistance is nonspecific.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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