A 72-year-old man with nephrotic syndrome undergoes renal biopsy. Light microscopy shows amorphous eosinophilic deposits in the mesangium and capillary walls. Congo red staining of the biopsy shows salmon-pink deposits. Under polarized light microscopy, these deposits show which characteristic finding?
- A Linear yellow fluorescence along the GBM
- B Birefringent calcium oxalate crystals
- C Apple-green birefringence ✓
- D Metachromatic purple staining
Correct answer: C. Apple-green birefringence
Explanation
Amyloid deposits in renal tissue are identified by Congo red staining, which shows salmon-pink color on light microscopy and pathognomonic apple-green birefringence under polarized light. This applies to both AL and AA amyloidosis. Linear yellow fluorescence is seen with immunofluorescence. Metachromatic staining and oxalate crystals are unrelated to amyloid identification.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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