Fact-sheet: Myocarditis


Updated on 11/12/2025 at 7:11 PM

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Definition

Inflammation of the myocardium combining cellular infiltrate and myocardial necrosis without significant coronary lesion, most often viral infectious (parvovirus B19, CMV, Coxsackievirus), more rarely non-viral (Borrelia burgdorferi, Trypanosoma cruzi) or drug-induced.

Clinical features

Nonspecific and variable clinical presentation:

  • Asymptomatic
  • Fever
  • Dyspnea
  • Palpitations
  • Chest pain
  • Heart failure
  • Sudden death

Viral context

Nonspecific ECG abnormalities (ST segment changes, T wave inversion)

Laboratory findings

Modest and nonspecific elevation of troponin and CPK

Radiography

Normal coronary arteries on coronary angiography

Ultrasound

Indirect signs and search for complications

  • Generally no significant abnormality of LV contractility or ejection fraction
  • Pericardial effusion
  • Rarely: segmental wall motion abnormalities
  • Left ventricular dysfunction
  • Reduced ejection fraction

CT

Assessment of myocardial enhancement at 5 minutes: subepicardial or mid-myocardial contrast uptake

Lower the kV (80) to increase contrast. Value of spectral CT

Normal coronary arteries on coronary CT angiography

MRI

Report elements:

  • Overall LV and RV dimensions and function, which are generally preserved. Description of regional wall motion abnormalities (cine)
  • Presence and location of myocardial edema (STIR, T2-mapping)
  • Early (hyperemia) / late (necrosis-fibrosis) enhancement
  • Subepicardial or mid-myocardial location
  • Extent: most often inferolateral-basal and mid-wall, 1 to 3 segments
  • Pericardial effusion / enhancement

Modified Lake-Louise diagnostic criteria = presence of both major criteria A and B:

  • A/ On T2: myocardial edema regional/global increase in myocardial signal on T2 STIR (myocardial signal intensity [SI] to skeletal muscle signal ratio ≥ 2.0)
  • increased T2 values on T2 mapping
  • B/ On T1 imaging: non-ischemic myocardial injury ± scar (necrosis-fibrosis) increased native T1 mapping values
  • Increased ECV mapping values
  • Late gadolinium enhancement with at least one focal lesion showing a non-ischemic regional distribution (subepicardial or intramyocardial)

Minor criteria, additional arguments supporting the diagnosis:

  • Segmental or global LV systolic dysfunction
  • Pericardial effusion

Associated RV dysfunction is a predictor of mortality, need for circulatory support, and heart transplantation. In fulminant Myocarditis, there is diffuse, severe, biventricular systolic dysfunction.

The extensive circumferential form (subendocardial or mid-myocardial) produces the "ring sign" pattern and should prompt investigation for arrhythmogenic cardiomyopathy or an underlying genetic cause (channelopathy with desmosomal gene mutations)

Repeat MRI 1 to 2 weeks after the initial examination if:

  • None of the criteria are present + very recent onset of symptoms and strong clinical evidence
  • Only one criterion is present

Nuclear medicine

Scintigraphy:

  • Gallium 67: nonspecific, myocardial inflammation
  • Antimyosin 111In: nonspecific, myocardial necrosis

Differential diagnosis

Myocardial infarction due to coronary stenosis