The incidence of myocarditis in children is uncertain but it is estimated that 1 per 100,000 children per year are affected. It has been reported that 0.05% of all pediatric hospitalizations are for myocarditis. Understanding the incidence of myocarditis is problematic because the disease is difficult to diagnose.
The “gold standard” method of making a diagnosis of myocarditis requires a biopsy of the heart muscle. This procedure can be risky in infants and small children. Some institutions are now using cardiac MRI to make the diagnosis. The MRI is less invasive and carries a different risk profile for very sick patients, but we do not know how reliable it is at making the diagnosis in children.
The signs and symptoms of myocarditis can be quite variable. Infants may show signs of listlessness, labored breathing and pallor. Frequently, they become disinterested in feeding or very fussy and difficult to console. Most older children will complain of abdominal or chest discomfort, fatigue or weakness. Respiratory symptoms such as increased work of breathing and wheezing may lead physicians to incorrectly diagnose children with asthma or pneumonia. It is not unusual for some patients to have experienced flu-like symptoms a few days or weeks before seeing a physician. Sometimes, sudden death is the first sign that something is wrong.
Treatment of acute myocarditis is mostly focused on supportive care. Symptoms of breathlessness or abdominal discomfort may be relieved with decongestive therapies such as diuretics. Features of low cardiac output or hypotension may be alleviated with inotropic/vasopressor infusions. In situations of cardiogenic shock, the utilization of mechanical circulatory support can be lifesaving. Although immunotherapies such as intravenous gamma globulin and steroids have been used in children with acute myocarditis, data have failed to demonstrate their benefit for survival or hospital readmission.
The prognosis of myocarditis in children depends, in part, on the age of the patient. The mortality rate in newborn infants has been reported as high as 75%, while estimates in older children generally range from 10-30%. If a child survives the early acute phase of the disease, their chances for long-term survival very good. In addition, some patients may develop a chronic or recurrent form of myocarditis. Pediatric patients hospitalized with myocarditis have a readmission rate of 15%.