A 68-year-old man has progressive exertional dyspnea with biventricular failure. ECG shows low voltage limb leads, echocardiogram shows biventricular thickening with granular sparkling of the myocardium, and there is carpal tunnel syndrome history. Endomyocardial biopsy confirms amyloid. Which stain establishes the diagnosis?

• A Periodic acid-Schiff
• B Prussian blue
• C Masson trichrome
• D Congo red with apple-green birefringence under polarized light ✓

Explanation

Cardiac amyloidosis is diagnosed by Congo red staining showing apple-green birefringence under polarized light, reflecting beta-pleated sheet fibril deposition. The combination of low voltage ECG with thick walls, sparkling myocardium, and carpal tunnel syndrome is classic for AL amyloid. Prussian blue detects iron (hemochromatosis), Masson trichrome stains collagen, and PAS stains glycogen, so none can confirm amyloid.

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.