Endomyocardial biopsy is the criterion standard for the diagnosis of myocarditis, including these conditions:
Adenoviral or enteroviral myocarditis
Human herpesvirus 6 myocarditis
Eosinophilic cell myocarditis
Checkpoint inhibitor-related myocarditis
Giant cell myocarditis
Idiopathic granulomatous myocarditis (cardiac sarcoidosis)
However, the use of routine endomyocardial biopsy in establishing the diagnosis of myocarditis rarely is helpful clinically, because histologic diagnosis seldom has an impact on therapeutic strategies, unless giant cell myocarditis is suspected. Nonetheless, the Heart Failure Society of America recommends considering endomyocardial biopsy for patients with acute deterioration of heart function of unknown origin that is not responding to medical treatment.
Elevated cardiac enzymes are an indicator for cardiac myonecrosis. Cardiac troponin (troponin I or T) in particular is elevated in at least half of patients with biopsy-proven myocarditis. Cardiac enzymes may also help to identify patients with resolution of viral myocarditis, but negative troponin findings do not exclude a diagnosis of myocarditis.
Antibody titer testing is not required for the diagnosis of viral myocarditis because of its low specificity and the delayed rising of viral titers, which would have no impact on therapeutic decisions. However, titers typically increase by fourfold in the acute phase and gradually fall during disease progression. Serial titers may be useful.
Antimyosin scintigraphy (using antimyosin antibody injections) can identify myocardial inflammation with high sensitivity and negative predictive power but has low specificity and low positive predictive power. In contrast, gallium scanning is used to reflect severe myocardial cellular infiltration and has a good negative predictive value, although specificity is low. PET has been used in selected cases (eg, sarcoidosis) to assess the degree and location of inflammation.
Read more on the workup of myocarditis.
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Cite this: Yasmine S. Ali. Fast Five Quiz: Myocarditis - Medscape - Dec 13, 2021.