The diagnosis of acute myocarditis is complex and challenging. The use of the Dallas
criteria in the diagnosis of myocarditis is associated with poor sensitivity and specificity
because of the sampling error related to the often focal distribution of the specific
histological lesions in cardiac tissue and the variability in pathological interpretation.
To improve histological diagnosis, additional virological evaluation of cardiac tissues
is required, with immunohistochemical and polymerase chain reaction (PCR) techniques
allowing identification and quantification of viral infection markers. The diagnostic
gold standard is endomyocardial biopsy (EMB) with the histological Dallas criteria,
in association with new immunohistochemical and PCR analyses of cardiac tissues. Using
real-time PCR and reverse transcription PCR assays, parvovirus B19, Coxsackie B virus,
human herpesvirus 6 (HHV-6) type B and adenovirus have been detected in 37, 33, 11
and 8% of EMB, respectively, from young adults (aged<35 years) with histologically
proven acute myocarditis. Viral co-infections have also been found in 12% of acute
myocarditis cases, generally parvovirus B19 plus HHV-6. Moreover, herpesviruses such
as the Epstein-Barr virus or cytomegalovirus can also be associated with myocarditis
after heart transplantation. During the clinical course of myocarditis, the immunohistochemical
detection of enterovirus, adenovirus or parvovirus B19 capsid proteins or herpesvirus
late proteins is necessary to differentiate a viral cardiac infection with replication
activities from a persistent or latent cardiac infection. These new viral diagnostic
approaches can lead to better identification of the aetiology of myocarditis and may
therefore enable the development and evaluation of specific aetiology-directed treatment
strategies.