Classification of amyloidosis: immunohistochemistry versus the potassium permanganate method in differentiating AA from AL amyloidosis.

As systemic AA and Al amyloidosis differ considerably with regard to prognosis and therapeutic approach, it is of importance to make an accurate histochemical classification with regard to the amyloid protein involved. In the present study the results of the potassium permanganate (KMnO4) method, an indirect histochemical procedure based on differences in cross-beta-potential of different amyloid fibril proteins, were compared with the results of an immunohistochemical method utilizing anti-AA and anti-AP antibodies. Renal biopsy sections of patients with systemic amyloidosis related to inflammatory conditions, systemic amyloidosis associated with plasma cell dyscrasia, idiopathic systemic amyloidosis, and nonamyloidotic controls were studied. Positive reaction of anti-AA was observed on all KMnO4-sensitive amyloid deposits, whereas the KMnO4-resistant amyloid deposits remained unstained, provided that highly purified anti-AA antiserum was used. Anti-AP produced not only comparable staining of both KMnO4-sensitive and -resistant amyloid deposits, but also of glomerular basement membranes and elastin layers of blood vessels in amyloid and control biopsies. The intensity of anti-AP reactivity was comparable with the reaction of anti-AA on KMnO4-sensitive amyloid deposits. The present results confirm the specificity of the KMnO4 method, which is a simple method available to every laboratory, in differentiating between AA and AL amyloidosis. Furthermore, the results indicate that, at least in renal biopsy specimens, anti-AP may serve as a general marker for AA and AL amyloid deposition; this finding is in contrast to the results of a recently published report.