Congo red staining of an amyloid-laden tissue viewed under polarized light shows which characteristic finding?
- A Metachromatic purple staining
- B Apple-green birefringence ✓
- C Bright red fluorescence
- D Yellow-brown pigment granules
Correct answer: B. Apple-green birefringence
Explanation
Amyloid stained with Congo red appears salmon-pink/orange on bright field microscopy, but under polarized light demonstrates pathognomonic apple-green birefringence due to the highly ordered beta-pleated sheet structure of amyloid fibrils. Metachromatic staining is seen with crystal violet or toluidine blue. This polarized Congo red staining is the gold standard for amyloid identification.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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