Myocarditis occurs when there is inflammation in the heart muscle. Giant-cell myocarditis (GCM) develops when this inflammation results in abnormal growth of cells. These then cause more inflammation to the heart, damaging it further. A number of conditions can lead to myocarditis. GCM, however, has no known cause.

GCM is a very rare medical condition that progresses rapidly. The abnormally large cells that it causes are collections of macrophages and lymphocytes, which play a role in inflammation and the functioning of the immune system.

Until the 1980s, people were likely to die within few months of receiving a GCM diagnosis. However, rapid treatment can prolong survival, and nowadays, 90% of people live for at least 1 year after diagnosis.

In this article, we look at the causes, risk factors, and symptoms of GCM. We also discuss treatment options, outlook, and related conditions.

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Myocarditis is an inflammation of the heart muscle that can result from a number of conditions. For example, it may be due to an infection when bacteria enter the bloodstream or when the immune system response causes inflammation.

However, doctors consider GCM idiopathic. This means they do not know what causes it and have not consistently found any similarities between people who have developed it.

Researchers have found a link between T lymphocytes and GCM. T lymphocytes are a type of white blood cell that plays an important role in the immune system.

Learn about different types of lymphocytes and what they do, here.

Who might develop GCM?

According to the National Organization for Rare Disorders (NORD), the median age for a GCM diagnosis is 42 years, which is an age at which other types of heart failure are rare. The condition affects males and females equally.

Doctors do not believe that GCM is genetic or that it can be due to behavioral factors.

NORD states that about 20% of people with GCM have autoimmune disorders, such as Crohn’s disease, which cause the body’s immune system to mistakenly attack healthy tissue. Some people have tumors in the thymus, an organ behind the breastbone.

Read a list of autoimmune diseases here.

Early symptoms of GCM, which are very similar to those of other heart issues, such as heart failure, include:

The most common symptoms of GCM may also present as other conditions, such as:

Rarely, this condition may result in sudden cardiac death.

Before the advent of heart transplants and modern medications that suppress the immune system, GCM was fatal. Most people lived less than 3 months after diagnosis.

Survival rates have improved, but GCM is still a progressive and highly deadly condition. A 2012 paper cites a small study involving 26 people who received medication to suppress the immune system, instead of a heart transplant. The survival rates were as follows:

  • 1 year: 69%
  • 2 years: 58%
  • 5 years: 52%

While a heart transplant may remedy symptoms, it is common for them to reoccur even in the new heart.

People who die of GCM may develop fatal heart arrhythmias, which make it impossible for the heart to pump blood throughout the body. Some people may die suddenly, without warning.

A GCM diagnosis can be a source of stress due to the data available on a person’s outlook. At this time, people may benefit from mental health support.

Learn about different types of mental health resources here.

A doctor can conclusively diagnose GCM with a heart biopsy. During this procedure, they use a needle to obtain a small sample of heart tissue to then examine it under a microscope to identify the giant cells.

However, GCM may mimic symptoms of other heart diseases. It is also a very rare condition, so it may not be the most likely explanation for the cardiac problems a person is having. For this reason, a doctor may order other tests as well, such as:

  • Blood tests: These can help detect troponin, whose presence in the blood can indicate heart damage.
  • Cardiac catheterization: This procedure involves threading a small, thin tube through the blood vessels to examine them along with the heart.
  • Electrocardiogram (EKG): Doctors use EKG to measure the electrical activity of the heart.

There are a number of treatment options that can help with GCM. They include:

Heart transplant

If the heart is severely damaged or if other treatments prove ineffective, a person may need a heart transplant.

The procedure can prolong a person’s life, but the wait is usually long, and symptoms can reoccur even in the new heart.

Heart implants

A pacemaker or defibrillator may help a person’s heart maintain a healthier rhythm longer.

Immunosuppressive therapy

Immunosuppressive therapy may prevent giant cells from attacking the heart. It can help a person live longer without a transplant, but it may also make them more vulnerable to infections.

People getting immunosuppressive treatments survive around 1 year on average after the onset of symptoms. Those who do not receive this type of treatment survive 3 months on average after the symptoms have started.

Supportive care

Other treatments, such as oxygen therapy, pain relief medication, and therapy to manage the stress of living with a serious illness, will not cure GCM or prevent its symptoms. They may, however, make it easier to live with a life threatening condition.

Learn what to expect during open heart surgery here.

There are numerous types of myocarditis, and the symptoms are similar. Treatment will vary depending on the type of myocarditis a person has. However, the risk of heart failure and death is present with all forms of myocarditis.

Lymphocytic myocarditis is very similar to GCM, as it also involves harmful inflammatory immune cells.

Some other conditions resembling GCM include:

  • Cardiac sarcoidosis: This is a complication of sarcoidosis. It causes the body to form harmful masses of inflammatory cells that may attack the heart and other organs.
  • Lymphocytic myocarditis: This rare condition develops when white blood cells cause inflammation in the heart muscle.
  • Hypersensitivity myocarditis: Some allergic reactions, for example to certain drugs, may cause inflammation of the heart muscle.
  • Congestive heart failure: This condition causes the heart to be less efficient at pumping blood throughout the body, usually due to damage over time. It is more common among older adults and people with behavioral risk factors for heart disease, such as smoking.
  • Atrial fibrillation (A-fib): This condition causes an irregular, rapid heartbeat due to abnormal electrical signals in the atria, which are the two upper chambers of the heart. People who have A-fib may experience a rapid heart rate, unusual heart rhythm, and shortness of breath. People with heart disease or heart health risk factors are more vulnerable to A-fib.

Learn about the different types of A-fib here.

GCM may be a scary diagnosis. Identifying it quickly is critical for prolonging a person’s life and ensuring they receive the most suitable treatment.

It is therefore important to contact a doctor immediately if a person experiences any heart symptoms, even if they are not at risk of heart disease.

Researchers are working to better understand the causes of the condition, and advances in diagnosis and treatment are currently underway.