What causes myocarditis?
Myocarditis can be caused by a variety of conditions such as a virus, sarcoidosis, and immune diseases (such as systemic lupus, etc.), pregnancy, and others. The most common cause of myocarditis is infection of the heart muscle by a virus. Doctors believe that viruses cause the initial muscle inflammation. After the initial viral infection subsides, the body's
immune system continues to inflict inflammatory damage on the heart muscles, prolonging the myocarditis, a process termed auto-immunity.
Viral infection - This common form of myocarditis often occurs after a viral infection of the nose and throat and often goes away on it own after it runs its course. Although many different viruses have the potential to produce myocarditis, coxsackievirus B is the most common culprit in the United States. Other viruses capable of causing myocarditis include echovirus, influenza (flu), Epstein-Barr, rubella, varicella (chickenpox), mumps and hepatitis.
HIV infection - About 10 percent of people with HIV develop myocarditis, either because HIV directly invades the heart muscle or because the patient's weakened immune system makes the heart muscle more susceptible to attack by other infectious agents, especially toxoplasmosis.
Bacterial infection - Rarely, myocarditis occurs as a complication of endocarditis, an infection of the heart valves and the lining inside the heart's chambers caused by bacteria. Some common bacteria responsible for myocarditis include Staphylococcus aureus, enterococci and Corynebacterium diphtheriae (the cause of diphtheria). In about 25 percent of people with diphtheria, a toxin (poison) produced by C. diphtheriae bacteria causes a form of myocarditis that leads to a flabby, stretched-out heart muscle. Because the flabby, enlarged heart cannot pump blood efficiently, severe congestive heart failure may develop within the first week of illness.
Chagas' disease - This infection, caused by the protozoan Trypanosoma cruzi, is transmitted by an insect bite. In the United States, myocarditis caused by Chagas' disease is most common among travelers or immigrants from Central and South America. In up to one-third of people with Chagas' disease, a form of chronic myocarditis develops many years after the initial infection. This chronic myocarditis leads to significant destruction of heart muscle with progressive heart failure.
Lyme myocarditis - Lyme disease, an infection caused by the tick-borne bacterium Borrelia burgdorferi, causes myocarditis or other heart problems in about 10 percent of patients.
Giant cell myocarditis - This rare form of myocarditis takes its name from large, abnormal giant cells that are found when a piece of the affected heart muscle is examined under a microscope. Giant-cell myocarditis is most common among patients suffering from thymoma (a growth of the thymus gland, which is a collection of immune system tissues below the top of the breastbone), systemic lupus erythematosus (SLE or lupus), or thyrotoxicosis (a very overactive thyroid), but its true cause remains a mystery. The illness usually strikes young adults, and it can quickly lead to death from heart failure and/or cardiac arrhythmia (abnormal heartbeat).
Other agents - Myocarditis also can be caused by alcohol, radiation, chemicals (hydrocarbons and arsenic), and drugs, including doxorubicin (Adriamycin, Rubex), cyclophosphamide (Cytoxan, Neosar), emetine, chloroquine (Aralen) and sulfonamides (Gantanol, Gantrisin, Thiosulfil Forte, Urobak). |
