Lmmunohistochemical classification of 140 autopsy cases with systemic amyloidosis

One hundred and forty autopsy cases of systemic amyloid-osis were examined using the potassium permanganate method for distinction of amyloid A protein from other amyloid proteins and an immunohistochemical technique. Of those cases, amyloid proteins were identified in 121 cases. There were 68 cases of amyloid A-related (AA) amyloidosis and these were the most common type among the cases (56.2%). There were 39 cases of immunoglobulin light chain-related (AL) amyloidosis (32.2%), six cases of β₂-microglobulin-related (Aβ2M) amyloidosis (5%), and five cases of transthyretin-related (ATTR) amyloidosis (4.1%). Minute areas of amyloid deposits in four cases with AA were resistant to potassium permanganate pretreatment. In Aβ2M amyloidosis amyloid deposits were either resistant or sensitive to potassium permanganate pretreatment, from case to case. The coexistence of two different amyloid proteins was seen in three cases: one case had ATTR and Ax types, and two cases had Aβ2M and AA types. Some discrepancies were seen between the immunohistochemical typing and clinical classification of amyloidosis referred to in the Annual of the Pathological Autopsy Cases in Japan, for example, one case of AA type in myeloma-associated amyloidosis and one case of AL type in secondary amyloidosis. From the present results, the importance of the immunohistochemical method in classifying amyloidosis is stressed.