INTRODUCTION Myocarditis is defined histologically as an inflammation of the myocardium associated with injury to cardiac myocytes (Fig. 1). Although many if not most cases of myocarditis remain idiopathic, a variety of treatable specific causes should be considered and excluded during the initial evaluation. These include infectious, autoimmune, toxic, and hypersensitivity reactions (Table 1). Myocarditis usually presents as an acute or fulminant illness, with new onset congestive heart failure and dilated cardiomyopathy. However, it may present as sudden death, acute myocardial infarc-
tion-like syndrome, new atrial or ventricular arrhythmias, or complete heart block.Occasionally, the physiologic presentation of acute myocarditis is more suggestive of a hypertrophic or restrictive than a pure dilated cardiomyopathy. Important clinicopathologic variants also include the endocardial eosinophilic and fibrotic diseases and pericarditis associated with focal of diffuse epicarditis (also called myopericarditis). In most acute cases of lymphocytic myocarditis, left ventricular function improves over one to six months with standard heart failure care. However a substantial minority will fail to clear a cardiotropic virus or develop persistent
Table 1. Common Causes of Myocarditis
Associated disorder or agent Clinical clues Diagnostic method Viral/Coxsackie B Flu-like prodrome Endomyocardial biopsy Acute rheumatic fever Jones criteria Throat culture, antistreptolysin O Lyme disease History of tick bite titer Doxorubicin/anthracycline Previous cancer treatment Serology Chagas disease Travel to Central or South America Clinical, endomyocardial biopsy Peripartum cardiomyopathy* Last trimester or first 6 mo postpartum Serology
inflammation that leads to chronic cardiomyopathy. In the patients who develop chronic cardiomyopathy, the risk of heart transplantation and death is high.