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Giant Cell Myocarditis

NORD is very grateful to Leslie T. Cooper Jr., MD, Director, Gonda Vascular Center; Professor of Medicine, Mayo Clinic, for assistance in the preparation of this report.

Synonyms of Giant Cell Myocarditis

  • GCM
  • idiopathic giant cell myocarditis

Disorder Subdivisions

  • No subdivisions found.

General Discussion

Giant cell myocarditis is a rare cardiovascular disorder that occurs for unknown reasons (idiopathic). It is characterized by inflammation of the heart muscle (myocardium), a condition referred to as myocarditis. Inflammation is caused by widespread infiltration of giant cells associated with other inflammatory cells and heart muscle cell destruction. Giant cells are abnormal masses produced by the fusion of inflammatory cells called macrophages. Individuals with giant cell myocarditis may develop abnormal heartbeats, chest pain and, eventually, heart failure. Many individuals eventually require a heart transplant. The disorder most often occurs in young adults.


The onset of symptoms of giant cell myocarditis is often rapid. Initial symptoms may include swelling of the ankles, chest pain, heart palpitations, fatigue, and shortness of breath (dyspnea) especially upon exertion or lying flat. Affected individuals eventually develop irregular heartbeats (arrhythmias) such as abnormally fast (tachycardia) or slow (brachycardia) heartbeats. Arrhythmias may cause sudden episodes of lightheadedness or loss of consciousness.

The abovementioned symptoms of giant cell myocarditis occur due to congestive heart failure or heart block. These two heart abnormalities are progressive and eventually result in life-threatening complications. In individuals with giant cell myocarditis, the average time from symptom onset to life-threatening complications or heart transplant is five and a half months.

The normal heart has four chambers. The two upper chambers, known as atria, are separated from each other by a fibrous partition known as the atrial septum. The two lower chambers are known as ventricles and are separated from each other by the ventricular septum. Valves connect the atria (left and right) to their respective ventricles. The valves allow for blood to be pumped through the chambers. Blood travels from the right ventricle through the pulmonary artery to the lungs where it receives oxygen. The blood returns to the heart through pulmonary veins and enters the left ventricle. The left ventricle sends the now oxygen-filled blood into the main artery of the body (aorta). The aorta sends the blood throughout the body.

Congestive heart failure is a condition in which abnormal enlargement or widening (dilatation) of one or more of the chambers of the heart results in weakening of the heart’s pumping action, causing a limited ability to circulate blood to the lungs and the rest of the body. This leads to fluid buildup in the heart, lungs and various body tissues. In some cases, all four chambers of the heart may be affected. Symptoms may include fatigue, shortness of breath (dyspnea) upon exertion, swelling of the legs and feet, and chest pain.

Heart block may be partial or complete. In the mild form of heart block (first degree), the two upper chambers of the heart (atria) beat normally, but the contractions of the two lower chambers (ventricles) slightly lag behind. In the more severe forms (second degree), not all of the atrial beats are conducted to the ventricles. In complete heart block (third degree), the atria and ventricles beat independently. Individuals with first or second degree heart block may not experience symptoms (asymptomatic). However, individuals with complete heart block may experience episodes of unconsciousness (syncope), breathlessness, and/or fatigue.


The exact cause of giant cell myocarditis is unknown. Approximately 20 percent of cases occur in individuals with autoimmune disorders suggesting that autoimmunity may play a role in the development of giant cell myocarditis. Autoimmune disorders are caused when the body’s natural defenses against "foreign" or invading organisms begin to attack healthy tissue for unknown reasons.

Autoimmune disorders associated with giant cell myocarditis include inflammatory bowel disease such as Crohn’s disease. Some cases of giant cell myocarditis have been associated with a tumor of the thymus (thymoma). The thymus is a relatively small organ behind the breastbone that is thought to play an important role in the immune system until puberty.

Affected Populations

Giant cell myocarditis affects males and females in equal numbers. It can affect individuals of any age although the majority of cases occur in young or middle-aged adults (median age 42 years). Approximately 300 cases have been reported in the medical literature.

Related Disorders

Symptoms of the following disorders can be similar to those of giant cell myocarditis. Comparisons may be useful for a differential diagnosis:

Cardiac sarcoidosis refers to the heart abnormalities sometimes associated with sarcoidosis, a rare disease characterized by the abnormal formation of inflammatory masses or nodules (granulomas) consisting of certain granular white blood cells (modified macrophages or epithelioid cells) in certain organs of the body. The range and severity of symptoms associated with sarcoidosis vary greatly, depending upon the specific organ(s) involved and the degree of such involvement. In some cases, only the heart may be involved (isolated cardiac sarcoidosis). The exact cause of sarcoidosis is not known. However, infectious, environmental, genetic, and immunological factors are under investigation as possible causes of the disorder. (For more information on this disorder, choose "sarcoidosis" as your search term in the Rare Disease Database.)

Lymphocytic myocarditis is a rare condition in which heart muscle inflammation (myocarditis) is caused by accumulation of white blood cells (lymphocytes). Symptoms may include chest pain, heart palpitations, fatigue, and shortness of breath (dyspnea) especially upon exertion or lying flat. Lymphocytic myocarditis is often caused by a virus.

Hypersensitivity myocarditis is a general term for inflammation of the heart muscle (myocarditis) that occurs due to an allergic reaction (hypersensitivity) to certain agents such as drugs. Symptoms may include chest pain, heart palpitations, fatigue, and shortness of breath (dyspnea) especially, upon exertion or lying flat. Some affected individuals may develop a rash or abnormal liver function studies.

Standard Therapies

A diagnosis of giant cell myocarditis is made by biopsy of heart tissue. A biopsy is a test in which small tissue sample is surgically removed and studied microscopically. Tests to exclude other cause of heart abnormalities may also be performed. These tests may include echocardiogram and cardiac catheterization.

Standard and supportive treatment options for cardiac failure and arrhythmias are recommended. These treatment options may include the insertion of a pacemaker or implantable heart defibrillator.

Affected individuals may require a heart transplant. Affected individuals are often evaluated for heart transplantation shortly after diagnosis. In 20-25% of cases, infiltration of giant cells has recurred after heart transplantation. Immunosuppresssion with drugs that include cyclosporine prolong survival free of transplantation. GCM can recur after therapy in both the native and allografted heart.

Investigational Therapies

Researchers are studying the use of immunosuppressive drugs combined with steroids to treat individuals with giant cell myocarditis. For more information contact:

Myocarditis Program at Mayo Clinic
200 First St. S.W.
Rochester, MN 55905
Phone: (507) 284-4441

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010

For information about clinical trials sponsored by private sources, contact:

Contact for additional information about giant cell myocarditis:

Leslie T. Cooper Jr., M.D.
Director, Gonda Vascular Center
Professor of Medicine
Mayo Clinic
200 First Street SW
Rochester, MN 55906

Giant Cell Myocarditis Resources

NORD Member Organizations:

(To become a member of NORD, an organization must meet established criteria and be approved by the NORD Board of Directors. If you're interested in becoming a member, please contact Susan Olivo, Membership Manager, at


Cooper LT Jr. Giant Cell Myocarditis. In: NORD Guide to Rare Disorders. Philadelphia, PA: Lippincott Williams & Wilkins; 2003:52-3.

Cooper LT Jr. Myocarditis. New England Journal of Medicine 2009;360:1526-38.
Cooper LT. Giant Cell Myocarditis in Children. Progress in Pediatric Cardiology. 2007;24:47-49.

Cooper LT, Okura Y. Idiopathic giant cell myocarditis. Curr Treat Options Cardiovasc Med. 2001;3:463-7.

Daniels PR, Berry GJ, Tazelaar HD, Cooper LT. Giant cell myocarditis as a manifestation of drug hypersensitivity. Cardiovasc Pathol. 2000;9:287-91.

Cooper LT. Giant cell myocarditis. Herz. 2000;25:291-8.

Cooper LT, Berry GJ, Shabetai R. Idiopathic giant-cell myocarditis/natural history and treatment. N Engl J Med. 1997;336:1860-6.

Myocarditis. May 2, 2012. Accessed June 28, 2012.

The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.

Report last updated: 2012/07/02 00:00:00 GMT+0

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