Medico-legal importance of myocarditis in causing death : histopathological study in Milan from 1993 to 2005

Introduction: under a pathological and a medico-legal point of view, myocarditis is a very interesting entity. Starting from macroscopic heart examination and anamnestic notes, the forensic pathologist can, through the inevitable step of microscopic evaluation, make a correct diagnosis of heart inflammation, being the pathologist able not only to find out the presence of a myocarditis, but to fully described it and grade it as well. Only a careful histological description of a present myocarditis can allow the pathologist to decide if it has been relevant in causing death. Methods: we considered 1591 consecutive cardiac samples (in toto) come to our attention from 1993 to 2005. After steps of 10% buffered formaline fixation and microscope slides creation (stains used: basic H&E, Mallory trichromic and histological Gram), we identified microscopically 95 cases of myocarditis. We made a careful histopathological analysis, focusing our attention on cellular and extra-cellular features (active myocarditis versus borderline myocarditis), dimension and topography of the inflamed site. For every case of our population, we made also a careful review of autopsy macroscopic notes (cardiac and extra-cardiac), anamnestic and historical notes (where possible) and results of toxicological assays. Results: our results underline the central role of microscopic evaluation in diagnosis and description of myocarditis. Microscopy is also the only instrument able to make a grading of the heart inflammation: only 17% of our 95 cases population was “positive or abnormal” at macroscopic cardiac evaluation, being the rest “negative or normal”. The present study shows that myocarditis is not as infrequent as someone may think. 19% of our inflammations (18 on 95) result cause of death, 41% are final steps of “multiple organ failure syndrome” and 40% (38 on 95) do not play any relevant role in causing death. Moreover, it does not exist a specific pre-mortal history that can help the pathologist to drive his attention to myocarditis as the cause of death. Conclusions: it is not enough to consider the rough macroscopic heart appearance to make diagnosis of myocarditis, to describe and to grade it. A normal heart at the macroscopic observation can be affected by a lethal myocarditis: this means that the pathologist, with a normal heart at autopsy, must keep in mind the chance of a myocarditis as cause of death and consequently has to make good samples from the heart for further microscopic evaluation. In our experience, “good samples” means to catch the whole heart for further histology. Microscopic study of the whole heart (and this alone!) can make careful heart mapping and then right myocarditis diagnosis, myocarditis description and finally myocarditis grading. Myocarditis as a cause of death is not as infrequent as an absent-minded pathologist can think (1% of unselected cases in our experience): the only way not to lose some right diagnosis is to know and to use a strict methodological approach, that starts at autopsy (right samples for histology) and come to microscope (careful heart mapping and grading).