What is giant cell myocarditis?

At some point in life, you may have heard the phrase ’heart disease.’ The fact is, heart disease is an umbrella term for all kinds of heart-related disorders, not just one disease. One of those diseases is myocarditis.

Myocarditis is the inflammation of the heart muscles (myocardium). Giant cell myocarditis is a variation that involves immune cells infiltrating into the heart tissue and causing damage.

But what does it mean to have giant cell myocarditis? Is it life altering or simply something you can ignore and move on? Well one thing is for sure, when it comes to concerns with the heart, they should never be ignored.

Overview

Giant cell myocarditis (GCM) is often attributed to inflammation that is caused by lymphocytes (a type of white blood cell that is part of the immune system).¹ This makes it an autoimmune disorder, meaning the immune system attacks the body’s own tissues.

Giant cell myocarditis is a type of myocarditis that is characterised by three main features:¹ 

• Fibrosis (excessive scar tissue formation)
• Necrosis (tissue or cell death)
• Multinucleated giant cells (lymphocytes that merge together to make one big cell)

Giant cell myocarditis is associated with various other autoimmune diseases and inflammatory conditions.²

Giant cell myocarditis is very rare.³ Giant cells appear as large singular cells. These come about when many inflammatory immune cells fuse together and form one large cell that secretes many chemicals, which end up damaging the heart muscle cells.⁴

The giant cells cause all sorts of damage, the main types being necrosis (cell death) and fibrosis (formation of fibrous tissue that is rigid and serves no purpose other than to act as a scar). Fibrosis also affects the elasticity of the heart muscles. This makes the heart pump inefficiently and causes it to eject less blood with every heartbeat.⁵

The damage to the heart can become so severe that the patient is required to have a transplant. This scenario often arises when the disease is diagnosed too late. Yet, the risk for giant cell myocarditis is still about 25% post-transplant.⁶

Giant cell myocarditis can be acute. This is the most fatal form of the disease, to the point that the patient’s survival for more than a year is rare without a transplant.⁷ 

Chronic giant cell myocarditis simply means that it takes a little longer to manifest, or that the symptoms may present after the patient has had an episode of acute myocarditis.  

Causes of giant cell myocarditis

The pathogenesis (disease development) of giant cell myocarditis is not yet fully understood, and as such, it can be difficult to diagnose in the early stages.⁶ 

Giant cell myocarditis is mainly considered to be autoimmune-mediated, often triggered by an infection. ‘Autoimmune mediated’ means that the immune system harms the body’s own heart. Immune cells infiltrate the heart muscles and identify and attack cells that may be diseased due to a recent infection, but the attack gets out of hand.⁸ 

In around 50% of myocarditis cases, the cause is unknown (also referred to as idiopathic).⁹ Aside from idiopathic cases, acute cases are mainly classified into two categories: those caused by infections and those of non-infectious origin.⁹ 

In cases where a cause has been identified, the main reason for the development of myocarditis was a viral infection (65% of all acute myocarditis cases).⁹ But this doesn't mean that other infections, which are of bacterial, parasitic or protozoan origin, cannot cause myocarditis. Simply, viruses are a more common cause.⁹

Signs and symptoms of giant cell myocarditis

The signs and symptoms of giant cell myocarditis are typically those of heart complications which include, but are not limited to:¹⁰

• Fatigue (tiredness)
• Palpitations (pounding/racing heartbeat without any logical reason)
• Angina (chest pain)
• Dyspnoea (difficulty breathing)
• Syncope (fainting for a short period of time)
• Cardiogenic shock (when blood supply is diminished to the organs because the heart is unable to pump the blood)
• Cardiac death (cardiac arrest/heart attack) 

There are other prodromal symptoms (symptoms or illnesses that appear a few weeks before the manifestation of actual disease-related symptoms) that are recorded in up to 80% of patients. These include the following:¹¹

• Fever
• Gastrointestinal symptoms
• Flu-like symptoms

Management and treatment for giant cell myocarditis

Once diagnosed, the usual treatment is the use of corticosteroids in combination with immunosuppressants.¹² These can help slow the progression of the disease and reduce the symptoms to improve overall health. Although corticosteroids may help in acute cases, long-term use may give rise to unwanted side effects. There is also the concern of drug interactions, which can be detrimental.¹³ 

Other treatments may include medication that addresses the symptoms caused by giant cell myocarditis, such as ventricular arrhythmia (irregularity in the heartbeat due to unusual contractions of the ventricle) and heart failure.

The key goal is for medication to help reduce the activity of giant cells, as well as to prevent new ones from forming to give the patient a better chance of survival.

Those who show abnormally large ventricles on medical scans will need external support to help the heart pump blood, which can be done using a machine called ECMO (extracorporeal membrane oxygenation).

If giant cell myocarditis has progressed and caused too much damage to the heart, a heart transplant (replacing the damaged heart with a healthy one from a donor) may be required. However, because of such few donors and the risk of not finding a compatible one, it may take a long time. 

Even after a successful transplant, a lot of care and treatment is needed post-surgery due to the risk of organ rejection and the development of graft-versus-host disease.¹² An electrocardiogram (ECG) can monitor the progress of the patient before (and after) the transplant. The ECG monitors electrical conductions and the heart’s overall ability to function. That way, doctors can manage any treatment necessary for the heart according to its condition.¹⁴

The patient is also advised to make lifestyle changes, like reducing stress and changing their diet, in order to manage the symptoms of giant cell myocarditis.

Diagnosis

As there are other forms of myocarditis and giant cell myocarditis is very rare, certain guidelines are used by doctors to diagnose giant cell myocarditis in particular.

A cardiac MRI scan is currently the gold standard for non-invasive diagnostic techniques.

A heart biopsy can also be used to confirm the diagnosis of giant cell myocarditis but this is an invasive procedure. The three main signs for the doctor to issue a heart biopsy to confirm giant cell myocarditis are as follows:¹¹

1. The patient indicates signs of a high-grade heart block
2. The patient’s echocardiogram indicates ventricular tachycardia (the lower chambers of the heart beating faster), also known as ventricular arrhythmia 
3. Despite the patient being given the proper care and medication, the patient fails to respond to the treatment and keeps getting worse

Heart tissue collected during the biopsy is examined by a pathologist, who looks at a thin layer of the sample under a microscope to search for giant cells, signs of necrosis (cell death) and fibrosis (which appears as pale yellow fibres).¹¹

FAQs

How can I prevent giant cell myocarditis?

Giant cell myocarditis cannot be prevented. The only measure that can be taken is for people who are at a high risk to monitor their health closely in order to catch the disease as early as possible to avoid excessive heart damage.

How common is giant cell myocarditis?

A large-scale study of autopsies indicated that the incidence of giant cell myocarditis is about 0.007% to 0.051%. However, this may be inaccurate because not every sudden cardiac death undergoes an autopsy, which in this case is crucial for diagnosis after death.¹⁵

Who is at risk of giant cell myocarditis?

There is not enough data to determine what age range is most at risk. However, as giant cell myocarditis is a disease instigated by immune cells, it can happen to anyone.

When should I see a doctor?

If you experience any heart-related symptoms, you should see a doctor immediately. These symptoms could include chest pain, difficulty breathing, palpitations and fainting. 

Summary

In conclusion, giant cell myocarditis is a very rare form of myocarditis (inflammation of the heart muscles). Medications, supportive care, and, in severe cases, heart transplantation are the treatment options for this disease. 

Identifying the disease at its earliest stage is key and doctors should be consulted to receive an accurate diagnosis, followed by appropriate treatment. Long-term multidisciplinary (immunology, cardiology and transplant) care is a necessity when it comes to giant cell myocarditis. This will ensure the patient can get the best possible prognosis and treatment. 

Regular check-ups and lifestyle changes can be key factors in how our bodies react to infections; they could be the difference between the body overreacting, leading to giant cell myocarditis, or simply curbing the infection and moving on as normal. However, those diagnosed with giant cell myocarditis need continuous treatment, care and monitoring for any signs of the condition worsening.