Myocarditis is a pathologic process characterized by inflammation of the myocardium leading to cellular necrosis and myocardial dysfunction. Although often thought of as a viral or post-viral process, causes of myocarditis are numerous and include infectious (viral, bacterial, fungi, yeast, rickettsial, protozoal, and parasitic) as well as non-infectious (toxins, drugs, autoimmune diseases, and Kawasaki disease) etiologies.
Cardiomyopathy is a general term referring to diseases of the myocardium. Clinically and pathologically, cardiomyopathy can be divided into dilated, hypertrophic, and restrictive types. As myocarditis is a precursor to and one of the causes of dilated cardiomyopathy, the two will be considered together.
The presentation of a child with dilated cardiomyopathy (DCM) depends on the age of the patient and the acuteness of the illness. Aggressive acute viral myocarditis may present as cardiovascular collapse and cardiac arrest over a very short period of time. Other causes of DCM in general, and occasionally myocarditis as well, may have a more progressive subacute to chronic course. Unless the disease process progresses to the point of causing significant myocyte necrosis and myocardial dysfunction, clinical symptoms may be absent. A slow decrease in ventricular function over many months or years may go unnoticed, whereas a rapid drop in ventricular function over several days may result in severe heart failure and cardiovascular collapse, as compensatory mechanisms have not set in. However, the chronic stable patient has little cardiac reserve, and therefore an unrelated illness such as an upper respiratory infection may result in cardiac decompensation. The history of an antecedent viral infection in the child presenting with a new-onset DCM may not herald the initiation of cardiac disease, as it is possible that the viral illness merely unmasked the chronic compensated form of DCM.
The usual presentation of DCM is that of congestive heart failure and low cardiac output. Signs and symptoms of heart failure and low cardiac output in newborns and infants include fussiness, poor appetite, poor feeding, fever, listlessness, diaphoresis, and respiratory distress. Physical examination generally demonstrates a patient with tachypnea, tachycardia, cardiomegaly, and hepatomegaly with pallor or an ashen appearance. The older child and adolescent will generally have a history of a viral illness 7 to 14 days prior to presentation with myocarditis. Findings of poor appetite and abdominal pain due to hepatic congestion, lethargy, exercise intolerance, malaise, and fever may also be present. Findings of heart failure including jugular venous distention and rales as well as low cardiac output may be present on physical examination in an older child, whereas the findings of rales and jugular venous distention are often absent in the newborn and infant.
The differential diagnosis of DCM based on age is seen in Table 55-1. All attempts should be made to diagnose the treatable causes of cardiomyopathy ...