Skin, Amyloidosis, Congo red stain

Amyloidosis is a disease of misfolded protein deposition in various tissues and organs, causing pressure atrophy of the surrounding cells and resulting in a wide array of clinical presentations. In this case, there was involvement of the skin (this biopsy), but also in the soft tissues of the tongue (see clinical history; image not included.)

On H&E (this slide), amyloid appears as a ring of amorphous, eosinophilic, hyaline substance surrounding the capillaries. Congo Red staining is obtained to confirm these deposits as amyloid (see related content). The amyloid deposits stain a pink colour under normal light, and more specifically produce an apple green birefringence under polarizing microscopy.

This slide shows Congo red stain. See related content for H&E stain.