Positive staining with Congo red in tissues with heat artifact due to cautery.

Congo red staining is rarely the source of false positives for amyloid. On the other hand, the heat artifact due to cautery in surgical specimens adopts some hyaline features, which can mimic amyloid deposits many times. Therefore, we decided to investigate the behavior of these artifacted areas with some of the ancillary techniques that are commonly used when diagnosing amyloidosis: Congo red staining (with and without treatment of the tissue by permanganate of potassium); Thioflavin T; polarized light and immunohistochemistry (for A amyloid, lambda chain and kappa chain). For that, 10 biopsies of different organs were selected with the condition that there was "evidence of heat artifact border". Our results showed that the artifacted border is strongly positive for Congo red (even after treatment with permanganate of potassium). It also showed apple-green birefringence when observed under polarized light. Nevertheless, it failed to express any of the markers investigated in the immunohistochemical study.