Myocarditis differential diagnosis

Overview
Myocarditis presents with chest pain and ST segment elevation. Myocardits must be distinguished from pericarditis and the life threatening condition of ST elevation myocardial infarction.

Differentiating Myocarditis from ST Segment Elevation Myocardial Infarction
Both diseases present with chest pain, elevated cardiac biomarkers, and focal left ventricular dysfunction. There are two studies that can be used to distinguish the two syndromes:

Coronary Angiography
Coronary angiography can be performed to distinguish myocarditis from ST segment elevation myocardial infarction. ST segment elevation myocardial infarction is associated with either complete or subtotal occlusion of an epicardial coronary artery on coronary angiography. When used in conjunction with the findings on coronary angiography, cMRI is useful in establishing the diagnosis of myocarditis. Among 79 patients with elevated cardiac biomakrkers who were suspected of having ACS and had normal coronary arteries on coronary angiography, 81% of the patients (including those with preserved ejection fraction) were diagnosed with myocarditis based on cMRI findings.

Cardiac Magnetic Resonance Imaging
Cardiac magnetic resonance imaging is also useful in distinguishing between the two syndromes as well. On cardiac MRI, myocarditis is associated with patchy, non-sentimental, hyperenhancement which is confined to the epicardial layer of the myocardium. In contrast, in ST segment elevation myocardial infarction there is confluent hyperenhancement extending from the endocardium in a distribution that mimics the distribution of the epicardial coronary arteries.

Differentiating Myocarditis from Pericarditis
Both diseases present with chest pain and ST segment elevation. The two conditions can be distinguished by the following studies:

Electrocardiogram
While both disorders are associated with ST segment elevation, pericarditis is also associated with PR segment depression.

Cardiac Biomarkers
Myocarditis is associated with elevations of the CK-MB and the troponin, while pericarditis is not. If pericarditis is associated with underlying inflammation of the myocardium, then this is called myopericarditis. If there is concomitant involvement of both the pericardium and myocardium in myopericarditis, then there are elevations of the cardiac biomarkers.

Echocardiography
In patients with myocarditis there will be a focal wall motion abnormalities, while these will be absent in the patient with pericarditis. There may be a pericardial effusion in the patient with pericarditis, while myocarditis is not associated with a pericardial effusion.