[Amyloid: microscopic demonstration, classification and clinical correlation]

Amyloid is a biophysically defined, biochemically non-uniform protein which is deposited in the tissue, forming a cross-beta configuration. In paraffin sections it is demonstrated using Congo red staining according to Puchtler et al. and a polarizing microscope with a tension-free clean optic system that shows a typical apple-green birefringence. The identification of amyloid has to be followed by immunostaining for AA, ATTR, A lambda, A kappa and A beta 2 microglobulin and possibly further types of amyloids for classification purposes. Considering the localization, expansion and type localized and generalized types probably can be differentiated. The latter should be correlated to a basic disease. The treatment of the basic disease is the only chance for reducing or eliminating the amyloid deposits. In this review, the modern morphological methods for demonstration and both immunohistological and clinical classification of amyloid and amyloidoses are presented. Rare types are mentioned in the tables.