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The diagnosis of myocarditis is difficult because there is no pathognomonic clinical presentation and the disease may mimic other non-inflammatory diseases. Thus, current classifications on cardiomyopathies (e.g., the World Health Organization and the International Society and Federation of Cardiology [WHO/ISFC], the European Society of Cardiology [ESC], and the 2013 Expert Myocarditis ESC Task Force) define myocarditis as an inflammatory disease of the myocardium, which is diagnosed on endomyocardial biopsy (EMB) based upon histological, immunological, immunohistochemical and molecular tools. This will identify etiology, and differentiate between infectious, mainly viral, and non-infectious, immune-mediated forms. The term "inflammatory cardiomyopathy" may be applied in biopsy-proven myocarditis with associated left, right or biventricular dysfunction. Myocarditis may resolve spontaneously, relapse or become chronic progressing to dilated cardiomyopathy, death or heart transplantation. The 2013 Myocarditis ESC Task Force consensus document recommends consideration of EMB and selective coronary angiography in all patients with clinically suspected myocarditis according to the Task Force criteria. It is recommended that EMB analysis includes not only histology (Dallas criteria), but also immunohistology and detection of the genome of infectious agents by molecular tools. EMB should be performed by expert teams. The rationale for this diagnostic effort is the availability of a wide range of immunosuppressive or immunomodulatory agents that, as shown in systemic extracardiac autoimmune disease and in many clinical studies, can be used in infection-negative myocarditis patients to stop or at least stabilize chronic cardiac tissue damage mediated by the immune system, and thus prevent fibrosis and progression to irreversible end-stage dilated cardiomyopathy.

Background: Human autoimmune myocarditis is characterized by an increased frequency of serum organ and disease-specific anti-heart autoantibodies (AHA) in affected patients. To assess whether AHA are directly pathogenic, we used the passive transfer technique of AHA from patients to normal Balb/c mice to induce an experimental myocarditis., Methods: In keeping with a classical passive transfer experiment, sera from 5 AHA positive myocarditis patients (3 male, mean age 30 ± 11 years, 3 with giant cell and 2 with lymphocytic myocarditis) were affinity purified and injected into 25 Balb/c mice. As controls, affinity purified sera from 5 healthy donors were passively transferred to 25 Balb/c mice. Further 15 control mice were injected with phosphate-buffered saline and 9 mice did not receive any injection. In all patients cardiac-specific AHA of IgG class had been previously detected by an indirect immunofluorescence (IFL) technique on cryostat sections of O blood group human heart. The animals were sacrificed after 4 weeks and the hearts were blindly examined for histological evidence of myocarditis by an expert cardiac pathologist., Results: Myocarditis was present in 13/25 (52%) of the mice which received affinity-purified IgG from patients. The findings of severe, moderate or mild myocarditis were more common in the mice which received affinity-purified IgG from patients (20%; 20% and 12%) than in control animals (2%, p=0.01; 0%, p=0.003; and 0%, p=0.04 respectively)., Conclusions: These findings provide a new evidence for AHA-mediated pathogenicity in human myocarditis, according to Rose-Witebsky criteria., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)