Myocarditis
- Lesion
Myocarditis is inflammation of the heart muscle that injures myocytes. Viruses are the commonest cause, but drugs, parasites and autoimmunity also cause it.
What it is
Myocarditis is inflammation of the myocardium with myocyte injury. In high-income countries most cases are viral (enteroviruses such as Coxsackie, adenovirus, parvovirus B19, SARS-CoV-2), causing direct damage and an immune response. Non-viral causes include Trypanosoma cruzi (Chagas, a major cause in Latin America), Lyme disease, diphtheria toxin, Toxoplasma, Trichinella, HIV, drug hypersensitivity, immune checkpoint inhibitors, rare mRNA vaccine reactions and autoimmune diseases. Giant-cell myocarditis is a rare, aggressive form.
Structure
- Gross: may be normal or dilated, flabby, with mottled pale and haemorrhagic areas.
- Microscopy: interstitial inflammation with adjacent myocyte injury; healed lesions leave patchy fibrosis.
Causes and patterns of myocarditis
| Type | Infiltrate | Notes |
|---|---|---|
| Viral (lymphocytic) | Lymphocytes with myocyte necrosis | Enteroviruses, adenovirus, parvovirus B19; may lead to dilated cardiomyopathy |
| Chagas disease | Mononuclear cells, parasite nests in acute phase, fibrosis in chronic | Trypanosoma cruzi; endemic in Latin America |
| Lyme disease | Lymphocytes and plasma cells near the conduction system | AV block that often resolves |
| Diphtheria | Little inflammation; toxin-mediated myocyte damage | Unvaccinated populations |
| Hypersensitivity and drug-induced | Eosinophils, lymphocytes, macrophages | Drugs, checkpoint inhibitors |
| Giant-cell myocarditis | Giant cells, lymphocytes, eosinophils, wide necrosis | Aggressive, autoimmune associations |
Clinical notes
- Presentations range from no symptoms to chest pain mimicking infarction, arrhythmias, acute heart failure or sudden death; troponin is elevated.
- Cardiac MRI shows edema and patchy late enhancement; biopsy is reserved for severe or atypical cases.
Test yourself
Think of the answer, then tap the question to see it.
What is needed to diagnose myocarditis on biopsy?
An inflammatory infiltrate associated with injury or necrosis of adjacent myocytes.
Which viruses are classic causes of myocarditis?
Enteroviruses, especially Coxsackievirus B; also adenovirus, parvovirus B19 and SARS-CoV-2.
Which form of myocarditis carries the worst prognosis?
Giant-cell myocarditis.
Elsewhere in DurgiPedia
- Cancer immunotherapy: checkpoint inhibitors, CAR-T and vaccines
- Type IV hypersensitivity (delayed, T cells)
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Myocarditis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.