Electron microscopy of primary and secondary cutaneous amyloidoses and systemic amyloidosis

Amyloid represents a broad group of chemically unrelated protein complexes that share uniform tinctorial and physical characteristics regardless of different pathogenetic mechanisms. Amyloid has long been identified by its histochemical properties, i.e., crystal violet metachromasia, violaceous appearance with periodic acid-Schiff reaction, positive staining with Congo red and Dylon, and dichroism of Congo red- and Dylon-stained sections on polarization microscopy. It has been further defined by its distinct fibrillar ultrastructures being comprised of 6 to 10-nm thick, straight, nonbranching, nonanastamosing filaments of indefinite length which have a tendency to aggregate as islands and run in random directions.