Highly sensitive diagnosis of amyloid and various amyloid syndromes using Congo red fluorescence

In order to find how best to diagnose amyloid deposits as early as possible , the sensitivity of three different methods that can be applied to the dia gnosis of amyloid in tissue sections have been compared: the Congo red stai ning method (CR), the combination of CR and immunocytochemistry (CRIC) and Congo red fluorescence (CRF). Tissue blocks were available from 25 patients , including 11 with immunohistochemically distinct and 3 with chemically un defined amyloid diseases. The results revealed (a) that CRF is more sensiti ve than either CR or CRIC, as shown qualitatively and quantitatively, (b) t hat CRF can therefore be utilized to track down even minute amyloid deposit s, which can be missed by the other two methods; (c) that the specificity o f CRF and CRIC is secured on double-stained sections by the demonstration o f green birefringence (GB) of the CRF-marked and IC-marked areas; (d) that CRF can be performed on the spot by just changing the light source; and (e) that CRF is ndt hampered by the congruent IC chromogen overlay, which ensu res the specific classification of the amyloid deposits as applied to diffe rent amyloid classes. In conclusion, CRF was demonstrated to be the most se nsitive method for direct diagnosis of amyloid in tissue sections. This met hod can, therefore, allow the earliest diagnosis and classification of amyl oid, which is a good basis for an amyloid class-specific therapy while orga n damage is still minimal.