Description

• Inflammatory disease of the myocardium. Viral infection is the most common cause. Other etiologies include infectious pathogens, autoimmune diseases, hypersensitivity reactions, systemic eosinophilic syndromes, and toxic reactions to drugs.
• Clinical presentation varies widely from mild chest discomfort or dyspnea, to shock, heart failure, and sudden cardiac death.
• Definitive diagnosis requires histologic or immunohistologic confirmation.
• Treatment is multifaceted and depends on the cause and severity of the disease. Options include basic pharmacologic therapy for left ventricular dysfunction, vasopressor, and inotropic support for hemodynamic compromise, immunomodulatory, immunosuppressive, antiviral therapy, extracorporeal membrane oxygenation, ventricular assist devices, and heart transplant for severely compromised patients.
• Often, there is a resolution of disease with supportive care. Unresolved disease may lead to chronic dilated cardiomyopathy (DCM) with risk of morbidity and mortality.

Epidemiology

• Male > female
• Infant mortality as high as 75%
• Child mortality as high as 25%

Incidence
Unknown, as endomyocardial biopsy (EMB) is infrequent due to risks and lack of histologic standard (1)

Prevalence

• Myocarditis is identified as the cause of DCM in approximately 10–15% of cases (2).
• Based on prospective postmortem data, myocarditis is associated with sudden cardiac death in young adults at rates between 4% and 20% (3).
• In HIV-related deaths, myocarditis is the most common cardiac finding on autopsy (50% prevalence) (1).

Etiology and Pathophysiology

Three-phase progression (4):

• Acute injury/infection: direct or indirect myocyte injury from pathogen or toxin and initiation of innate immune response
• Subacute phase/myocardial inflammation: acquired immune system activation with immune dysregulation. T-cell response, B-cell activation, and possible antibody cross-reaction with endogenous myocardial epitopes (molecular mimicry) lead to myocytolysis and worsening inflammatory response.
• Chronic: progression to DCM; immune response downregulation and development of fibrosis in the myocardium
• Viral
  • Coxsackie B, cytomegalovirus, HIV and adenovirus most common
• Bacterial
  • Staphylococcus, Streptococcus, Mycoplasma
• Fungal
  • Aspergillus, Candida, Coccidioides, Cryptococcus
• Protozoal
  • Trypanosoma cruzi, Entamoeba histolytica
• Parasitic
  • Schistosomiasis, larva migrans, trichinosis
• Spirochetal
  • Borrelia burgdorferi, leptospirosis, syphilis
• Immunologic
  • Giant cell, sarcoidosis, Kawasaki disease, systemic lupus erythematosus (SLE)
• Hypersensitivity reactions
  • Cephalosporins, colchicine, lithium, diuretics, sulfonamides
• Systemic hypereosinophilic syndromes
• DRESS syndrome
• Thyrotoxicosis
• Toxins
  • Ethanol, cocaine, heavy metals, carbon monoxide, envenomation

Risk Factors

• Prior hypersensitivity reactions
• Autoimmune disease
• Drug or toxin exposure
• Living in or traveling to an area endemic to specific pathogens
• Eosinophilic syndromes