Etiology

• Viral infections (most common): The leading cause in developed countries; commonly associated with enteroviruses, adenovirus, parvovirus B19, human herpesvirus 6 (HHV-6), influenza viruses, and SARS-CoV-2.

• Bacterial infections: Less common; may occur secondary to pathogens such as Corynebacterium diphtheriae, Borrelia burgdorferi (Lyme disease), Mycoplasma pneumoniae, and other bacterial infections.

• Autoimmune and inflammatory diseases: Includes systemic lupus erythematosus (SLE), rheumatoid arthritis, systemic vasculitides, inflammatory bowel disease, and other immune-mediated disorders.

• Drug-induced hypersensitivity myocarditis: May develop as an immune-mediated reaction to medications, including immune checkpoint inhibitors, certain antibiotics, anticonvulsants, and other drugs.

• Toxin-related myocarditis: Caused by exposure to alcohol, cocaine, amphetamines, heavy metals, radiation, or other cardiotoxic agents.

• Giant cell myocarditis: A rare but highly aggressive autoimmune form characterized by rapidly progressive heart failure and malignant ventricular arrhythmias.

• Cardiac sarcoidosis: Granulomatous myocardial inflammation that may present with conduction abnormalities, ventricular arrhythmias, or heart failure.

Risk Factors

• Recent viral infection, particularly involving the respiratory or gastrointestinal tract.

• Pre-existing autoimmune or systemic inflammatory disease.

• Immunosuppression, including HIV infection, malignancy, or immunosuppressive therapy.

• Young age, particularly adolescents and young adults, who are more commonly affected.

• Exposure to cardiotoxic medications or recreational drugs, including chemotherapy agents and cocaine.

• Family history of autoimmune disorders or inherited susceptibility to immune-mediated diseases.

• Male sex, which is associated with a higher incidence of myocarditis, particularly viral myocarditis.