Myocarditis is focal or diffuse inflammation of the cardiac muscle (myocardium). It may be acute or chronic and can occur at any age. Frequently, myocarditis fails to produce specific cardiovascular symptoms or electrocardiogram (ECG) abnormalities, and recovery is usually spontaneous, without residual defects. Occasionally, myocarditis is complicated by heart failure; rarely, it may lead to cardiomyopathy.
Myocarditis may result from:
viral infections (most common cause in the United States and western Europe): coxsackievirus A and B strains and, possibly, poliomyelitis, influenza, rubeola, rubella, and adenoviruses and echoviruses
bacterial infections: diphtheria, tuberculosis, typhoid fever, tetanus, and staphylococcal, pneumococcal, and gonococcal infections
hypersensitive immune reactions: acute rheumatic fever and postcardiotomy syndrome
radiation therapy: large doses of radiation to the chest in treating lung or breast cancer
chemical poisons: such as chronic alcoholism
parasitic infections: especially South American trypanosomiasis (Chagas’ disease) in infants and immunosuppressed adults; also, toxoplasmosis
helminthic infections: such as trichinosis
medications: penicillin, ampicillin, hydrochlorothiazide, methyldopa, and sulfonamides (may cause hypersensitivity myocarditis)
autoimmune factors: human immunodeficiency virus (has been shown to directly attack the myocardium)
rejection syndrome: rejection of posttransplant hearts (may cause inflammatory myocarditis).