Lindee Abe, ARNP
Myocarditis is a problematic diagnosis. There is not one test or symptom that leads to the
diagnosis. Instead, it is a combination of the history, physical exam, and diagnostic findings that
show the provider the diagnosis. It is not a common diagnosis, making it challenging to consider
in the list of differentials. However, this diagnosis is crucial because it can lead to poor outcomes
if left untreated.

Overview
Myocarditis is the inflammation of the myocardium or cardiac muscle. Myocarditis can
be due to various causes, both infectious and noninfectious. It can also be acute, subacute, or
chronic. The chart below highlights the many different sources of myocarditis. These lists are not
all-inclusive, as this highlights some possible causes of myocarditis:
Infectious Causes
Viral | Adenovirus, Arbovirus, Cytomegalovirus, Epstein-Barr virus, Herpesvirus, HIV, Influenza, Hepatitis B & C, Rabies, Small pox vaccine, Varicella, Yellow fever |
Bacterial | Chlamydia, Clostrodial, Gonococcal, Legionella, Meningococcal, Pneumococcal, Salmonella, Staphylococcal, Streptococal, Tuberculosis |
Spirochetal | Leptospirosis, Lyme disease, Syphillis |
Myotic | Aspergillosis, Candiasis, Histoplasmosis |
Protozoal | Chagas disease, Leishmaniasis, Malaria, African Sleeping Sickness, Toxoplasmosis |
Rickettsial | Q fever, Rocky mountain spotted fever, Typhus |
Helminthic | Ascariasis, Filariasis, Schistosomiasis, Strongyloidiasis, Trichinosis |
Noninfectious Causes
Cardiotoxins | Alcohol, Arsenic, Carbon monoxide, Catecholamines, Cocaine, Heavy metals, Radiation |
Hypersensitivity reactions | Antibiotics, Clozapine, Diuretics, Dobutamine, Insect bites, Lithium, Methylodopa, Snake bites, Tetanus toxoid, Vaccinations |
Systemic disorders | Celiac disease, Collagen-vascular disorders, Inflammatory bowel disease, Kwasaki disease, Sarcoidosis, Thyrotoxicosis |
Presentation
Myocarditis is different than pericarditis, which is the inflammation of the pericardium.
It can result in more severe outcomes than pericarditis. Myocarditis and pericarditis sometimes also occur together, which is referred to as myopericarditis. Myopericarditis occurs when the
inflammation from the pericardium extends into the myocardium and is manifested through an
elevated troponin. Myopericarditis is treated the same way as pericarditis. Perimyocarditis is
pericarditis with a decreased left ventricle function. Perimyocarditis should be treated the same
as myocarditis.
Myocarditis is more common in males than females. One theory surrounding this finding
is that estrogen has a protective effect against cardiomyopathy. Likewise, the incidence of myocarditis in males was 6.1 in 100,000 vs. 4.4 in females between the ages of 35-39 years. The most
commonly affected age group is 20-50 years of age.
The clinical presentation of myocarditis is variable, which is what makes it such a difficult diagnosis to make. It is theorized that there are more cases than diagnosed due to many subclinical cases. Patients with symptoms < 3 months are diagnosed with acute myocarditis, while patients with symptoms > 3 months are diagnosed with chronic myocarditis.
Symptoms of Myocarditis
Symptoms of myocarditis can include fatigue, chest pain, arrhythmias, cardiogenic shock, heart failure, and also dyspnea. Typically, there will be a history of a viral illness before the onset of cardiac symptoms. I have seen a patient who had a viral disease the week prior, and although the fever had resolved and had no signs of dehydration, they were still tachycardic.
In this case, it would be easy to attribute the tachycardia to a viral illness. However, if other disease symptoms resolve and the patient is still tachycardic, it should be investigated further. The key to diagnosing myocarditis is to keep the diagnosis in your differential diagnoses and be cautious when abnormal findings, like tachycardia, don’t fit the clinical picture.
It is not uncommon for patients with myocarditis to not present until they begin to have heart failure. This can manifest as fatigue and dyspnea. The patient may have edema, jugular vein distention, and also hepatomegaly on physical exam. This can quickly progress to cardiogenic shock. If the primary age group is 20-50, myocarditis may present as a younger, otherwise healthy patient with edema of the legs.
Diagnosis
When diagnosing myocarditis, the diagnostic work-up should always include ECG, cardiac markers, and chest x-ray. ECG may have abnormal findings or can also be normal. Abnormal findings on EKG include single atrial or ventricular ectopic beats, nonspecific ST changes, and complex ventricular arrhythmias. The ECG findings can also be similar to pericarditis or acute MI, which makes it difficult to distinguish between the diagnoses. Chest X-ray may show cardiac enlargement and pulmonary congestion but is generally nonspecific.
Cardiac troponin is usually elevated, especially if symptoms are present for < 1 month. Likewise, cardiac troponin is frequently used to help distinguish between myocarditis and pericarditis. However, the absence of cardiac troponin elevation does not exclude the diagnosis of myocarditis. Additional lab work should include CBC, creatinine, electrolytes, LFTs, ESR, CRP, and also BNP. An echocardiogram is also recommended in all patients to evaluate the heart’s function. Additional diagnostic imaging may include coronary angiography or cardiovascular magnetic resonance (CMR).
Cardiac biopsy and histology are the gold standard for diagnosing myocarditis. However,
in patients that are considered low-risk, “clinically suspected myocarditis” may also be diagnosed
with clinical presentation and diagnostic findings. Specifically, CMR can be used for diagnosis.
Clinical Course of Myocarditis
The clinical course is variable for patients with myocarditis. Some patients will also have
myocarditis resolved without intervention. Other patients will have prolonged hospital stays.
Several criteria were predictive of worse outcomes in patients with myocarditis:
- LVEF < 50%
- Sustained ventricular arrhythmias
- Low cardiac output syndrome requiring inotropes or mechanical circulatory support
- Presence of cardiac-specific antibodies
Treatment for myocarditis will vary based on the severity of the illness and also the underlying
cause of the myocarditis. General treatment will include treatment for heart failure and
arrhythmias. Patients should be instructed to avoid NSAIDs, exercise, and alcohol until
myocarditis is resolved. Therefore, IV fluids should be administered cautiously. Regardless of the severity of the illness, all patients will require a follow-up echocardiogram every three months.
Summary
Myocarditis is not a common diagnosis and is challenging to detect. The presenting
symptoms are similar to many other illnesses and can therefore be easily misdiagnosed. Although some cases of myocarditis can be self-limiting, other cases can be fatal, making it a vital diagnosis not
to miss. The vital principle remains for myocarditis that is essential for many other diagnoses-if
the symptoms don’t completely fit the diagnosis, then you should reevaluate your diagnosis.
References:
Cooper LT. Clinical manifestations and diagnosis of myocarditis in adults. Post TW, ed.
UpToDate. UpToDate Inc. Accessed October 19, 2023. https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-ofmyocarditis-in-adults
Cooper LT. Treatment and prognosis of myocarditis in adults. Post TW, ed. UpToDate.
UpToDate Inc. Accessed October 19, 2023.
https://www.uptodate.com/contents/treatment-and-prognosis-of-myocarditis-inadults?search=myocarditis%20treatment&source=search_result&selectedTitle=1~150&u
sage_type=default&display_rank=1#H200957324
Imazio M. Myopericarditis. Post TW, ed. UpToDate. UpToDate Inc. Accessed October 19, 2023. https://www.uptodate.com/contents/myopericarditis?search=myocarditis&topicRef
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