What stain demonstrates amyloid deposits?

• A. Congo red with apple-green birefringence under polarized light.
• B. Hematoxylin and eosin.
• C. Luxol fast blue.
• D. Silver stain.

Answer: (A)

Amyloid deposits are best demonstrated with Congo red staining. When tissue containing amyloid is stained with Congo red and viewed under polarized light, the deposits show an apple-green birefringence, a distinctive and diagnostic feature due to the beta-pleated sheet structure of amyloid binding the dye.

Hematoxylin and eosin is a general stain that can reveal extracellular material but is not specific for amyloid, so it cannot confirm amyloid on its own. Luxol fast blue targets myelin and is used for demyelinating processes, not amyloid. Silver stains highlight various structures like reticular fibers or basement membranes and fungi, but they do not selectively reveal amyloid.