The spectrum of myocarditis: from pathology to the clinics

Myocarditis is an inflammatory disease of the myocardium, which may occur in isolation or as part of systemic infectious/immune/autoimmune conditions, characterized by vast aetiologic, clinical and histopathologic heterogeneity. The broad spectrum of myocarditis can be categorized according to the prevalent histopathologic pattern including lymphocytic, lympho-histiocytic, eosinophilic and neutrophilic forms, giant cell myocarditis and myocarditis with granulomata. Diverse histopathologic substrates generally reflect different aetiologies and pathogenetic mechanisms and may be critical to clinical decision-making. Active vasculitis, when present, completes the inflammatory spectrum. Unfortunately, the correlation of histopathologic patterns, clinical presentation and disease course in myocarditis is still largely unresolved, due to limited availability of bioptic samples at specific stages of disease and impracticality of serial sampling. We here review the elements supporting an aetiology-driven diagnostic work-up in myocarditis, emphasizing the importance of integrating pathologic studies with clinical features and information derived from multimodality imaging. Furthermore, we explore myocardial inflammation in genetic cardiomyopathies, its role in driving clinical variability and the potential of transcriptomic and proteomic analysis in our understanding of these complex interrelations.