Key points
- Myocarditis, an inflammation of the myocardium, is classified as idiopathic in more than 50% of patients. Other causes include viruses or bacteria, various toxins including alcohol, or those causes secondary to a coexisting systematic disease such as HIV or lupus erythematosus
- Although myocarditis often resolves spontaneously without treatment, some patients present with heart failure, cardiogenic shock, or cardiac arrhythmias, all of which require urgent treatment as appropriate
- Diagnosis is complicated owing to the highly variable clinical presentation of myocarditis and the difficulty in providing laboratory confirmation of the diagnosis and etiology. Blood troponin I (TnI) and creatine kinase (CK)-MB cardiac enzyme levels and imaging studies such as echocardiography or magnetic resonance imaging (MRI) may be helpful, but a myocardial biopsy remains the gold standard
- Treatment includes therapy targeted at the cause of myocarditis if an infectious agent or toxic substance, and supportive therapy aimed at the clinical manifestations such as congestive heart failure and arrhythmias. Multiple treatment approaches for viral myocarditis are currently under evaluation. In particular, immunoglobulin and immunosuppressive therapy have shown promise in selected small clinical trials
- Prognosis depends on both the individual patient and the causative agent. Overall mortality rates vary. The Myocarditis Treatment Trial, currently the largest clinical study to evaluate long-term prognosis of myocarditis, showed a 20% mortality rate at 1.0 year and a 56% mortality rate at 4.3 years
- Urgent antitoxin treatment may be indicated in cases in which myocarditis is caused by the Corynebacterium diphtheriae bacteria
Background
Description
- Myocarditis is an inflammation of the myocardium. In more than 50% of patients, the cause is unknown
- Has a highly variable clinical presentation ranging from asymptomatic to rapidly progressive and fatal congestive heart disease
- Accounts for 20% of sudden cardiac deaths in adults younger than age 40 years
- Endothelin-1 plays an important pathophysiological role in myocarditis as with other cardiovascular disorders
- Prognosis is good in the majority of patients although it is substantially worse in the very young and elderly
- Experimental data on antiviral and immunotherapy have shown some promise to be effective in viral myocarditis
Epidemiology
Incidence and prevalence
- Difficult to determine; the majority of patients are clinically silent and resolve spontaneously without treatment
- Highly variable incidence owing to differences in methods used for diagnostic evaluation. One estimate has been 8 to 10 cases per 100,000 of the U.S. population
- The prevalence of myocarditis among unselected autopsy series is as high as 1% to 5%
- The prevalence of viral myocarditis is variable and is related to the periodic cycle of viral epidemics
- A recent study pointed out that myocarditis is a frequently underdiagnosed disorder. Viral RNA was detected in a large amount of biopsy samples obtained from patients that were initially diagnosed as idiopathic dilated cardiomyopathy (IDCM). These findings suggest that viral myocarditis is frequently the etiology of heart failure in patients who were initially identified as having IDCM using current standard diagnostic techniques
Demographics
Age:
- Average age of patients with myocarditis is 42 years; mean age of patients with giant cell myocarditis is older—58 years
- Younger patients are prone to more severe illness
Gender:
- Male-to-female ratio is 1.5:1.0
Genetics:
- Unknown. Certain individuals can be genetically predisposed to myocarditis
Geography:
- Infectious agents vary by location. One common cause of myocarditis in developing countries is Trypanosoma cruzi, which causes Chagas disease. It is endemic to Central and South America. There is, however, regional predominance of other infectious agents, for example, T cruzi is predominant in South America; group B coxsackievirus is predominant in North America and Europe. Several causative agents of myocarditis exhibit regional differences in prevalence such as the ticks that transmit Borrelia burgdorferi, the causative agent of Lyme disease
Socioeconomic status:
- A lower socioeconomic status is a risk factor for a number of infections known to cause myocarditis including diphtheria and HIV
Causes and risk factors
Causes
Common causes:
- Myocarditis is idiopathic in 50% of cases
- Viral etiologies vary by geographical region: group B coxsackievirus, adenovirus, parvovirus B19, echovirus, influenza virus, Epstein-Barr virus, HIV, rubella virus
- Rheumatic fever
Rare causes:
- Bacterial such as Chlamydia pneumoniae, Mycoplasma pneumoniae, B burgdorferi, Clostridium perfringens, C diphtheriae toxin, tuberculosis
- Protozoal such as Chagas disease
- Fungal such as candida, aspergillus, and histoplasma
- Metabolic such as pregnancy, thyroid disease, thiamine deficiency, or amyloidosis
- Toxins such as arsenic, carbon monoxide, hydrocarbons, phosphorus, mercury, cobalt, and lead
- Posttransplantation cellular rejection
- Medications such as anthracyclines, phenothiazines, penicillin, streptomycin, anticonvulsants such as phenytoin and carbamazepine, and cocaine
- Smallpox vaccination
Serious causes:
- Patients with myocarditis as a manifestation of an underlying rheumatic disease such as rheumatoid arthritis, autoimmune disease, or systemic inflammatory disease such as SLE have a worse prognosis
- Myocarditis caused by an immune response to infection by group B coxsackievirus can lead to dilated cardiomyopathy
- Posttransplantation cellular rejection
Risk factors
- Immunosuppression
Associated disorders
Inflammation of the pericardium (ie, pericarditis) or the endocardium (ie, endocarditis).
Screening
Not applicable.
Primary prevention
Summary approach
Most cases of myocarditis cannot be easily prevented; however, precautions can be taken.
Population at risk
- Immunosuppressed patients
- Patients with potential exposure to agents known to cause myocarditis
Preventive measures
Environment:
- Protective measures introduced at the work environment will reduce exposure to toxins such as arsenic, carbon monoxide, or lead, would likely reduce the prevalence of toxin-related myocarditis
- DEET-containing insect repellents and sensible attire should be used in tick-infested areas
Medication history:
- Phenothiazines, penicillin, streptomycin, and antiepilepsy drugs such as phenytoin and carbamazepine have been associated with a risk of myocarditis. These drugs should therefore be used with caution and dose reduction or drug withdrawal should be considered if signs of myocardial inflammation occur
- Prompt treatment of causative diseases may also reduce the risk of developing myocarditis
Immunization:
