Lethal cardiac amyloidosis: Microscopic differential diagnosis with microfibrillar cardiomyopathy in a forensic case.

In a previous study, we presented a case of an elderly woman's sudden death, in which microscopic examinations showed intramyocardial eosinophilic material suspected for amyloid, but not definable as such to the classic Congo Red staining. To overcome the arisen interpretative and diagnostic difficulties, we experimentally modified the classic Congo Red staining, using a specific one for corpse. The finding of a low-intensity positivity allowed us to formulate a very likely diagnosis of occult lethal cardiac amyloidosis. However, this low-intensity positivity obtained after having applied this experimental method for the first time and in only one case, as well as the existence of the rare pathology known as microfibrillar cardiomyopathy, which may be related to the observed microscopic findings, have forced us to investigate the correctness of the diagnosis. For this purpose, we performed in-depth investigations with sodium sulphate-Alcian Blue (SAB) staining and immunohistochemistry. Thanks to them, the amyloid nature of the intramyocardial material was confirmed and has been proved not only the reliability of our experimentally modified technique, but also the appropriateness of the diagnosis previously formulated. Therefore, the supposed involvement of the microfibrillar cardiomyopathy was excluded.