Differentials
Acute coronary syndrome
SIGNS / SYMPTOMS
Patients presenting with myocardial infarction tend to be older and have traditional risk factors for coronary atherosclerosis when compared with patients with myocarditis.
INVESTIGATIONS
Left heart catheterisation should reveal significant coronary atherosclerotic disease.
Dilated cardiomyopathy
SIGNS / SYMPTOMS
There can be considerable overlap between dilated cardiomyopathy and myocarditis. As many as 16% of patients presenting with acute dilated cardiomyopathy who undergo endomyocardial biopsy are found to have biopsy-confirmed myocarditis.[70]
A family history of dilated cardiomyopathy, a known history of exposure to a direct cardiotoxin (e.g., ethanol), or the absence of elevations of markers of myocardial injury make myocarditis less likely.
INVESTIGATIONS
The presence of an inflammatory infiltrate of the myocardium with necrosis and/or degeneration of adjacent myocytes not typical of the ischaemic damage associated with coronary artery disease is diagnostic for myocarditis. However, the lack of these findings does not exclude myocarditis.
Pericarditis
SIGNS / SYMPTOMS
It can be difficult, if not impossible, to distinguish patients presenting with pericarditis from those with myocarditis based on history and physical examination alone.
Both syndromes can exhibit typical or positional chest pain, and both are commonly preceded by a fever and/or a viral syndrome.
The presence of signs or symptoms of heart failure suggests myocarditis as the aetiology, as isolated pericarditis does not impair left ventricular (LV) function.[16]
INVESTIGATIONS
Two-dimensional echo can be used to help differentiate these conditions. The presence of LV dysfunction (systolic or diastolic) implicates myocarditis as the aetiology.
Stress-induced cardiomyopathy (broken heart syndrome, Takotsubo cardiomyopathy)
SIGNS / SYMPTOMS
Patients with stress-induced cardiomyopathy can present similarly to those with acute myocarditis.
A history of an acute emotional or physical stressor within the prior 2 weeks with a rather rapid clinical deterioration supports a diagnosis of stress-induced cardiomyopathy.[71]
Rapid recovery back to baseline within 4-8 weeks is the rule for stress-induced cardiomyopathy, the occurrence of which supports its diagnosis.
INVESTIGATIONS
No specific test will distinguish stress-induced cardiomyopathy from myocarditis.
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