Comparative study of Congo red fluorescence and immunohistochemistry in cutaneous amyloidosis

Background: Detection of amyloid can be done by several techniques either histochemical or immunohistochemical. Among them, one of the less mentioned in texts of reference and in reports on amyloidosis, is the examination with ultraviolet light of the stain of Congo red. We intend to examine cases of amyloidosis stained with Congo red with ultraviolet light and to see if such method offers advantages with respect to Congo red only and to immunohistochemistry. Material and Methods: We examined 12 cases of cutaneous amyloidosis Hematoxylin-Eosin, Congo red stains (with and without permanganate treatment), Thioflavin T and immunohistochemical stains. We also evaluated Congo red fluorescence (CRF). Results: 66.66% were women and 33.34% were men. The traditional methods for the detection of amyloid (Congo red and Thioflavin T) were positive in 87.50% while immunohistochemistry was positive in 100% of the cases. In one case, immunohistochemistry detected Congo red negative deposits of amyloid. In another case, immunohistochemistry was strong while CRF was weak. CRF was always weak in all the cases in which it was seen. Conclusions: Immunohistochemistry is superior in the detection of cutaneous amyloid over the other techniques tested. CRF did not result, in our experience, to be so useful.