Myocarditis - classification, etiology, pathogenesis, and clinical manifestations.
Myocarditis is inflammation of the heart muscle (myocardium), often resulting in myocyte necrosis and cardiac dysfunction.
Classification
By cause
By histology
Etiology
Infectious (most common)
- Viruses: Coxsackievirus B, adenovirus, parvovirus B19, HIV.
- Bacteria: Corynebacterium diphtheriae, Borrelia burgdorferi (Lyme disease).
- Parasites: Trypanosoma cruzi (Chagas disease), Trichinella spiralis.
- Fungi: Candida, Aspergillus (in immunocompromised).
Non- infectious
- Autoimmune diseases (SLE, systemic sclerosis).
- Rheumatic fever (post- streptococcal).
- Hypersensitivity (drugs: antibiotics, antiepileptics).
- Toxins (alcohol, chemotherapeutic agents like doxorubicin).
Pathogenesis
- 1 Initial trigger
- Direct myocardial injury by infectious agent or immune-mediated mechanisms.
- 2 Innate and adaptive immune responses
- Viral antigens presented → T- cell activation.
The immune system also releasescytokines, which are chemicals that help coordinate inflammation.
Activated cytotoxic T cells attack and destroy infected myocytes in an attempt to clear the infection.
- 3 Myocyte necrosis
- Direct cytopathic effect (viral replication inside myocytes, causing them to burst (lysis). ) and immune-mediated destruction - T cells and inflammatory substances kill infected cells but can also harm neighboring healthy cells, increasing overall cell death (necrosis).
- 4 Healing or progressio n
- In some cases → resolution and full recovery.
- In others → chronic inflammation → fibrosis → dilated cardiomyopathy and chronic heart failure.