Examples of Inflammatory and Infiltrative Myocardial Diseases
Inflammatory and infiltrative myocardial diseases represent distinct pathophysiologic categories that can overlap clinically, with inflammatory diseases primarily involving immune-mediated myocardial damage (viral myocarditis, giant cell myocarditis, cardiac sarcoidosis) and infiltrative diseases characterized by abnormal substance deposition in the myocardium (amyloidosis, sarcoidosis, hemochromatosis). 1
Inflammatory Myocardial Diseases
Infectious Myocarditis
- Viral myocarditis is the most common inflammatory myocardial disease, caused by cardiotropic viruses including enteroviruses, adenoviruses, parvovirus B19, human herpesvirus 6, and SARS-CoV-2 1, 2, 3
- SARS-CoV-2 has emerged as a major cause, with autopsy studies showing classic myocarditis in 7.2% of COVID-19 deaths and some form of cardiac inflammation in 47.8% 3
- Bacterial myocarditis can occur with direct bacterial invasion or as part of systemic bacterial infections 4, 5
- Protozoal myocarditis, particularly Chagas disease caused by Trypanosoma cruzi, affects 13% of the at-risk population in endemic areas, with one-third developing chronic heart disease 1
- Fungal myocarditis occurs primarily in immunocompromised patients 4
Autoimmune/Immune-Mediated Myocarditis
- Giant cell myocarditis is a rare, rapidly fatal autoimmune condition requiring aggressive multidrug immunosuppression, as this approach has shown improved survival 2, 3
- Eosinophilic myocarditis (Loeffler endocarditis in nontropical regions) is part of hypereosinophilic syndrome (eosinophils >1,500/mm³ for >6 months), with cardiac involvement in 50% of patients 1
- Myocarditis associated with systemic autoimmune diseases including rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis 1, 6
- Hypersensitivity myocarditis triggered by drugs or allergic reactions 4, 7
Important Clinical Caveat
Most viral myocarditis cases are self-limited with complete recovery, as cardiac dysfunction is usually reversible 2, 3. However, the American College of Cardiology definitively showed through the Myocarditis Treatment Trial that immunosuppression with prednisone plus azathioprine or cyclosporine provides no benefit in typical lymphocytic (viral) myocarditis 2. Immunosuppression should only be used for giant cell myocarditis and cardiac sarcoidosis, not for routine viral myocarditis. 2
Infiltrative Myocardial Diseases
Diseases Causing Myocardial Thickening
- Cardiac amyloidosis (AL type or transthyretin-related ATTR type) results in myocardial and valvular thickening, presenting with heart failure or arrhythmia 1
- Anderson-Fabry disease causes glycosphingolipid accumulation in the myocardium 1
- Acute sarcoidosis presents with myocardial thickening in the early inflammatory phase 1
- Danon disease is a lysosomal storage disorder causing myocardial hypertrophy 1
- Myocardial oxalosis presents with left ventricular thickening, heart block, and conduction abnormalities 1
- Mucopolysaccharidoses has variable phenotypic expression with glycosaminoglycan accumulation 1
- Friedreich ataxia is characterized by mitochondrial iron accumulation, with cardiomyopathy in 63% of patients 1
Diseases Causing Myocardial Thinning
- Chronic sarcoidosis results in myocardial thinning after the acute inflammatory phase resolves 1
- Scleroderma involves the heart in 80% of autopsy cases, manifesting as heart failure, arrhythmia, coronary artery disease, or sudden death 1
- Iron overload cardiomyopathy (siderotic cardiomyopathy) is characterized by iron deposition from frequent blood transfusions and altered iron hemostasis in hemoglobinopathy patients, presenting with heart failure, conduction abnormalities, or sudden death 1
Cardiac Sarcoidosis: A Disease with Both Features
Cardiac sarcoidosis uniquely bridges inflammatory and infiltrative categories, characterized by myocardial infiltration with noncaseating granulomas 1. Myocardial involvement occurs in 25% of patients with systemic sarcoidosis in the United States 1. It presents with conduction abnormalities, arrhythmias, sudden cardiac death, heart failure, pericardial effusion, or ventricular aneurysms 1. The American Heart Association recommends corticosteroids as first-line therapy, with alternative immunosuppressive agents for steroid-intolerant patients 2.
Special Considerations in Autoimmune Disorders and Cancer
Autoimmune Disease Context
- Patients with rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis are at increased risk for inflammatory myocarditis 1, 6
- Scleroderma has particularly high cardiac involvement (80% at autopsy) and should be actively screened 1
- Systemic sarcoidosis patients require cardiac evaluation given 25% myocardial involvement rate 1
Cancer-Related Considerations
- Endomyocardial fibrosis occurs in the context of hypereosinophilic syndrome, which can be associated with hematologic malignancies 1
- Cardiac amyloidosis (AL type) is associated with plasma cell dyscrasias and multiple myeloma 1
- Chemotherapy and immunotherapy can cause drug-induced myocarditis in cancer patients 4
Diagnostic Approach
Endomyocardial biopsy remains the gold standard for definitive diagnosis when life-threatening clinical course requires consideration of immunosuppression 2, 3. However, infiltrative disease is generally evaluated with history, clinical examination, ECG, serology, and imaging tests, with biopsy reserved for cases requiring definitive diagnosis 1. Cardiac MRI is a sensitive, non-invasive diagnostic tool that can confirm acute myocarditis and guide biopsy decisions 2.