Amyloid Typing: Immunoelectron Microscopy

The diagnosis of amyloidosis requires that amyloid deposits are demonstrated in patient’s tissues. Congo red staining is still the most commonly used method to detect amyloid deposits. Nevertheless, the results of Congo red stain may be ambiguous, especially if it is performed in centers with limited expertise in its execution and/or interpretation. Furthermore, Congo red stain does not provide any information concerning the nature of amyloidogenic protein. The characterization of amyloid proteins by light microscopic immunohistochemistry in paraffin-embedded samples frequently yields nonspecific results. Based on our experience at the Amyloid Center and Pathology Unit of IRCCS Policlinico San Matteo/University of Pavia, the ultrastructural examination of abdominal fat aspirate and other tissue biopsies is capable of confirming or ruling out a diagnosis of amyloidosis and can detect even very small deposits of amyloid fibrils. Moreover, immunoelectron microscopy can correctly characterize the amyloidogenic protein in all the commonest forms of amyloidosis, i.e., AL, AA, ATTR, Aβ 2 M, and AApoAI.