Acute myocarditis is a potentially life-threatening inflammatory disorder of the myocardium, most commonly caused by viral pathogens such as coxsackie A and B, as well as influenza viruses and other enteroviruses, but an array of infections and autoimmune etiologies have been described. Chest pain, dyspnea, and syncope are principal symptoms. The clinical course, however, varies from asymptomatic to sudden cardiac death. A comprehensive clinical workup comprised of laboratory, imaging, and microbiological studies are necessary to make the diagnosis.
Acute myocarditis (AM) is defined as an inflammatory disease involving the myocardium and its exact pathogenesis model remains to be completely elucidated    . AM can arise on the grounds of various infections and autoimmune disorders    . By far, viruses are responsible for the majority of cases, primarily enteroviruses (coxsackie A or B and echoviruses), but also Epstein-Barr virus (EBV), hepatitis C virus (HCV), and increasingly important human herpesvirus 6 (HHV6) and parvovirus B19, which were recently identified as the main causes of myocarditis in Germany   . In addition, bacteria (Brucella spp., Clostridium spp., Francisella spp., Legionella, etc.), fungal microorganisms (Aspergillus, Candida, Cryptococcus, Histoplasma), and a number of parasites have been reported as a cause of myocarditis as well  . On the other hand, sarcoidosis, Wegener's granulomatosis, celiac disease, connective tissue disorders, rheumatic fever, but also various drugs (antimicrobials, diuretics, antipsychotics, etc.) are notable non-infectious etiologies of myocarditis  . The clinical presentation starts with a flu-like symptomatology (fatigue, malaise, and constitutional symptoms), followed by dyspnea, palpitations, arrhythmias, and chest pain with discomfort as the main symptoms  . However, patients may be completely asymptomatic or develop severe cardiac insufficiency that results in heart failure and sudden death, and up to 9% of all sudden cardiac deaths have been attributed to myocarditis in certain reports   . Tachycardia, cardiogenic shock, and a syndrome mimicking myocardial infarction (MI) or coronary heart disease (CAD) can be seen in severe cases  . Although the short-term prognosis of acute myocarditis is generally good , long-term sequelae in the form of cardiomyopathy and progressive decline in cardiac functions are observed  , thus illustrating the importance of an early diagnosis and proper treatment.
The life-threatening nature of AM necessitates a thorough diagnostic workup, starting with a detailed patient history that will identify the course and progression of symptoms, recent travel (to exclude certain viral, fungal or parasitic infections), and the presence of comorbidities that may contribute to clinical deterioration. The physical examination is perhaps even more important, which can reveal tachycardia, cardiac murmurs (soft S1 sound, S3 or S4 gallop, as well as sounds pointing toward insufficiency of the mitral or tricuspid valve), a pericardial friction rub, and a displaced punctum maximum  . A full body inspection must not be overlooked, as it may lead to findings such as lymphadenopathy, subcutaneous nodules, joint sensitivity (typical for sarcoidosis and rheumatic fever, respectively) or other signs of that might point to the underlying cause . As soon as the heart is identified as the source of symptoms, cardiac enzymes: troponin I, troponin T, and creatine kinase-MB (CK-MB) must be evaluated to exclude myocardial infarction, after which electrocardiography (EKG) and imaging studies, primarily cardiac ultrasonography, should be employed . Although clear diagnostic criteria do not exist for acute myocarditis, an overall reduced activity of the myocardium (hypokinesia) is the main finding, but more importantly, other etiologies (valvular or congenital heart disease, as well as myocardial infarction) can be ruled out  . Extensive microbiological testing is available, mainly through serology and blood cultures, but the introduction of molecular testing (eg. polymerase chain reaction, or PCR) has markedly improved the overall success of identifying microorganisms in patient samples . Endomyocardial biopsy is a definite method for confirmation of AM, but it is indicated only if the procedure is assumed to have a vitally important effect on the therapeutic course    .