Microfocal myocardial lesions in cardiac allograft recipients

Endomyocardial biopsy has been widely accepted as a method for diagnosing acute heart transplant rejection. However, disperse and microfocal changes due to a smaller specificity, cause difficulty in histological differential diagnosis. The purpose of the present study was to morphologically assess microfocal lesions, to determine their relative incidence and their specificity in relation to the time of onset after cardiac transplantation and to compare these data with those concerning more extensive changes. We examined 658 samples in 152 endomyocardial biopsies obtained from 45 posttransplant patients, including 311 samples identified as containing focal lesions of varying size, and 33 as containing diffuse lesions. Samples with focal and diffuse lesions (344 samples) were submitted for further studies which revealed that microfocal changes in the transplanted heart show more enhanced polymorphism in the composition of cellular infiltrates than more extensive changes. Furthermore they are frequently seen in biopsies in the first two months after transplantation and as single changes. Necrosis and cellular infiltrates at that time are more diversified than those seen in later biopsies. In our experience differential diagnosis of microfocal myocardial lesions in cardiac allograft recipients is difficult. Potentially microfocal lesions may be a result not only of acute rejection but also a result of myocardial alterations in the course of intensive therapy both in the donor and in the recipient, cold ischemia, reperfusion, and inflammation. The morphological picture in some cases is not sufficient to make an unequivocal diagnosis. This indicates the need for improvement of diagnostic methods and criteria on the one hand, and a suitable approach to the problem on the other hand. Our experience shows that a temporary solution could be establishing of a separate classification category for these types of changes and defining them as nonspecific microfocal lesions.