What is the most common cause of myocarditis?

Most Common Cause of Myocarditis

Viral infections are the most commonly identified cause of myocarditis, particularly in North America and Western Europe. 1

Epidemiology and Regional Variations

Viral myocarditis has significant regional variations in prevalence:

• In North America and Western Europe, viral infections predominate as the leading cause 1
• In specific world regions, other important causes include:
  • Chagas disease (Latin America)
  • Poststreptococcal rheumatic heart disease (developing countries)
  • HIV (areas with high prevalence)
  • Diphtheria (reported in Afghanistan and India)
  • Typhoid fever, rubella, and even scorpion bites (parts of Asia) 1

The reported prevalence of viral myocarditis is variable, estimated at 10 to 106 cases per 100,000 people worldwide, with an annual incidence of approximately 1.8 million cases 1.

Specific Viral Pathogens

Among viral causes, the predominant pathogens vary by region:

• In Western Europe, the most frequent viral causes are:

  • Parvovirus B19
  • Human herpes virus 6 1

• Other important viral pathogens include:

  • Coxsackie B and other enteroviruses (particularly important in acute and fulminant myocarditis) 1, 2
  • Almost two dozen different viruses have been linked to myocarditis 1

Non-Viral Causes

While viral infections are the most common etiology, other causes include:

• Bacterial infections
• Protozoal infections
• Toxins
• Drug reactions
• Autoimmune diseases
• Giant cell myocarditis
• Sarcoidosis 3

These non-infectious causes are collectively less common than infectious causes but can be clinically significant in specific demographic groups, particularly because they may respond to immunomodulatory therapy 1.

Clinical Implications

The clinical presentation of viral myocarditis varies widely:

• Can range from subclinical cases to sudden cardiac death 4
• Symptoms may include fever, dyspnea, cough, and chest pain 1
• Additional symptoms: postexertional fatigue, palpitations, and syncope 1
• Viral coinfection with ≥2 viruses occurs in a substantial minority of cases 1

Diagnostic Considerations

Diagnosis can be challenging due to:

• Absence of specific pathognomonic features
• Wide spectrum of clinical manifestations 4
• Regional variations requiring careful travel and exposure history 1

Cardiac MRI is crucial for diagnosis, with findings typically showing:

• Subepicardial or mid-myocardial fibrosis
• Late gadolinium enhancement in a non-coronary distribution pattern 4
• Edema during acute inflammation 4

Treatment Approach

Treatment strategies depend on the cause and severity:

• Standard heart failure therapy for most patients 3
• Immunosuppressive agents may be beneficial in non-infectious cases 2
• Intravenous immunoglobulin has been used in some cases 2
• Antiviral agents may be considered for specific viral etiologies 2
• In severe cases, mechanical circulatory support or heart transplantation may be indicated 3

The prognosis is generally good in acute viral myocarditis, except in cases of giant cell myocarditis, which tends to be more aggressive 3.