High prevalence of chronic myocarditis in dilated cardiomyopathy referred for left ventriculoplasty: expression of tenascin C as a possible marker for inflammation.

The objectives of this study were to analyze the incidence of chronic myocarditis in dilated cardiomyopathy and to evaluate the diagnostic value of tenascin C for assessing inflammatory activity in the resected myocardium. Dilated cardiomyopathy patients with chronic myocarditis have a poor clinical outcome despite recent advances in medical treatments. Therefore, a precise diagnosis of inflammatory activity is critical to ensuring appropriate therapy. Tenascin C is an extracellular matrix glycoprotein that plays an important role in tissue remodeling in various heart diseases. Myocardial samples obtained during left ventriculoplasty from 64 patients (50 +/- 13 years, 56 men and 8 women) with dilated cardiomyopathy were examined by immunostaining for tenascin C. Histologic diagnosis was based on the Dallas criteria modified by the International Society and Federation of Cardiology task force. Nine cases (14%) had active myocarditis, 21 (33%) had borderline myocarditis, and 34 (53%) had no myocarditis. Intense tenascin C expression was observed at the site of active inflammation, with abundant cell accumulation, and in organized granulation tissue during the resolving phase but not in scar tissue during the healing phase. The ratio of tenascin C-positive area to the whole myocardium in the active and borderline myocarditis groups was significantly greater than that in the noninflammatory group. These findings suggest a high prevalence of chronic myocarditis in dilated cardiomyopathy patients and that tenascin C may prove to be a useful marker for distinguishing inflammatory cardiomyopathy from other types of dilated cardiomyopathy.