MRI for the Diagnosis and Follow-Up of Myocarditis
To the Editor:
We read with interest the elegant study by Friedrich and associates1 about the usefulness of MRI in the evaluation of myocardial changes in acute myocarditis. The authors evaluated the variation in T1-weighted sequences with gadolinium enhancement over time in 19 patients with clinically suspected myocarditis. In 7 patients, an endomyocardial biopsy (EMB) was also performed, and the morphological pattern was compared with the MRI acquirements to assess correlation between the 2 diagnostic tools. They conclude that contrast-enhanced, T1-weighted sequences performed during the first 2 weeks after the onset of symptoms elucidate the evolution of the inflammatory process from a focal to a diffuse myocardial disease. They also state that T2-weighted sequences yield a poorer-quality image, with signal intensity being not statistically different from controls.
In contrast, it has been our experience2 that MRI T2-weighted sequences are able to discern patients with or without myocarditis. We are currently performing a study on 75 consecutive pediatric patients with symptoms of acute congestive heart failure, left ventricular enlargement with depressed systolic function, and no evidence of congenital heart disease. All children were submitted to both EMB and MRI. The invasive study identified 51 patients with acute myocarditis and 24 dilative cardiomyopathies. Compared with the gold-standard EMB, our MRI images, based on T2-weighted sequences, achieved a sensitivity of 100% and a specificity of 90% (Gagliardi, unpublished data, 1998). It must be noted that 2 patients with negative EMB but positive MRI were actually affected by myocarditis, which was later correctly diagnosed on the basis of their clinical outcome. An EMB sampling error was probably the cause of these 2 “false false-positives” at MRI, reinforcing the opinion of a higher diagnostic accuracy of MRI with respect to EMB in the early, focal phase of myocarditis.1
The resulting 53 children affected by myocarditis have been submitted to repeated EMB and MRI every 6 months to evaluate the efficacy of MRI in identifying persistent, resolving, or resolved myocarditis during a 2-year follow-up period. Our preliminary data3 confirm the usefulness of MRI evaluation of signal intensity increase with T2-weighted sequences during follow-up, because its sensibility and specificity remain high throughout the entire evolution of the disease. It is also interesting to note that during follow-up, the results of EMB do not take into account the reduction of the extension of the inflammatory process on the entire ventricle. Conversely, MRI (recording signals from the entire ventricle, both right and left) provides more precise information about the presence and the extension of the inflammatory process. This approach is particularly useful when the evolution of signal intensity variation is being evaluated in the single patient over time.
We conclude with Friedrich et al1 that the use of MRI during the early phase and the follow-up of myocarditis provides highly reliable clinical information while decreasing risk and discomfort related to invasive procedures.
- Copyright © 1999 by American Heart Association
Friedrich MG, Strohm O, Schulz-Menger J, Marciniak H, Luft FC, Dietz R. Contrast media–enhanced magnetic resonance imaging visualizes myocardial changes in the course of viral myocarditis. Circulation. 1998;97:1802–1809.
Gagliardi MG, Bevilacqua M, Di Renzi P, Picardo S, Passariello R, Marcelletti C. Usefulness of magnetic resonance imaging for diagnosis of acute myocarditis in infants and children, and comparison with endomyocardial biopsy. Am J Cardiol. 1991;68:1089–1091.
Gagliardi MG, Polletta B, Di Renzi P, Giannico S, Bassano C, Ragonese P. Follow-up of myocarditis in pediatric age: magnetic resonance imaging or endomyocardial biopsy? Circulation. 1996;94(suppl I):I-181. Abstract.
We are grateful to Gagliardi and coworkers for their valuable comment on our study. They correctly stress the important role of T2-weighted MRI in patients with acute myocarditis. Because heavy T2 weighting leads to an almost exclusive signal of water-bound protons, myocardial edema should be easily visualized by this technique. As we pointed out in our article, because of the impaired quality of the conventional T2-weighted images, we were not able to detect a significant difference in patients compared with controls. However, in the same article, we report preliminary results in 6 patients with significant changes in T2-weighted breath-held images.R1 We have since continued this study using a heavily T2-weighted breath-holding MR sequence (STIR, or Short T1 Inversion Recovery) in the same scanner (Siemens Magnetom Expert 1.0 T). The skeletal muscle was used as an internal reference, and a ratio of global myocardial to skeletal muscular signal was calculated. In contrast to 13 volunteers, there were areas of a strong myocardial signal in all 11 patients during the follow-up of acute myocarditis. The ratio of global myocardial to skeletal muscular signal was significantly higher on days 7, 14, 28, and 84 after the onset of symptoms but not on day 2. Because this technique is a “water image,” the stronger signal observed in patients most likely represents edema due to inflammation. Thus, visualization of edema seems to be a reasonable approach in visualizing acute myocarditis. However, this phenomenon was not present very early after the onset of the disease. Furthermore, myocardial damage may persist after the edematous phase, and the disease activity may be missed by just T2-weighted MRI. We are currently evaluating the use of both breath-held T2, for visualizing edema, and contrast-enhanced T1 to detect edema and cellular damage. Both techniques may give additive information on the disease process. Our initial data suggest that this approach is a fast and reliable noninvasive technique to establish or exclude acute or subacute myocarditis. We encourage Gagliardi and colleagues to continue their important work.
Friedrich M, Strohm O, Schulz-Menger J, Marciniak H, Luft FC, Dietz R. Contrast media-enhanced magnetic resonance imaging visualizes myocardial changes in the course of viral myocarditis. Circulation. 1998;97:1802–1809.