Myocarditis and look-alikes: when the diagnosis matters

Myocarditis is an inflammatory disease of the heart muscle that can be triggered by various causes, including viruses, autoimmune response, molecular mimicry and exposure to immune-stimulating drugs or vaccines. Most cases of myocarditis heal, and cardiac dysfunction, if present, recovers; however, selected forms may require targeted therapy to improve outcomes. We herein review five conditions presenting with or mimicking myocarditis that require targeted diagnostic approaches, including endomyocardial biopsy, and/or targeted treatments. Giant cell myocarditis is an intense and unresolving inflammation of the heart, characterised by rapid progression, significant arrhythmias, heart failure and shock, that is unlikely to resolve without immunosuppression therapy. Myocarditis related to immune checkpoint inhibitors is a rare but potentially fatal adverse effect of the use of cancer immunotherapy with checkpoint inhibitors, requiring immunosuppressive therapy. Eosinophilic myocarditis can be triggered by allergy, hypersensitivity reactions, infections or can be idiopathic and is characterised by eosinophilic infiltrates in the heart and other organs, associated with thrombosis and necessitating targeted therapy. Myocarditis is a frequent cardiovascular manifestation of systemic immune-mediated inflammatory diseases such as systemic lupus erythematosus, and injury is caused by an autoimmune response in the myocardium and cytokine-mediated damage, requiring targeted therapy. Genetic pathogenic mutations in desmoplakin and other desmosomal genes can present with 'hot phases' mimicking myocarditis associated with an increased risk of arrhythmias, heart failure, and sudden cardiac death.