OBJECTIVE: To determine whether immunohistochemical analysis of cardiac biopsies from patients presenting clinically as dilated cardiomyopathy (DCM) show a chronic inflammatory process. DESIGN: Comparative case control study. SETTING: Tertiary referral centre. PATIENTS: Biopsies from 170 patients with DCM and 85 control patients with other cardiac diseases. RESULTS: Nine patients had sufficient interstitial inflammatory cells to be called borderline myocarditis on conventional histology, leaving 161 patients with DCM. In 78 patients with DCM (48%) there were T lymphocytes in the myocardium. In 48 (62%) of these 78 T lymphocyte densities were in the range 2-14 per high power field (HPF), equivalent to 7-50 per mm2 of tissue. In 43 (89%) interstitial and endothelial immune activation was demonstrated by MHC expression. In 30 patients with T cell counts in the range 1.5-2.0 per HPF, 80% also showed endothelial activation. Lymphocyte density correlated with increased expression of MHC class I and II antigens and the adhesion molecules ICAM, VCAM, ELAM, LFA-3, and GMP140. In all control biopsies the T lymphocyte density was less than 1.0 per HPF (less than 2-5 per mm2 of tissue). CONCLUSIONS: Nearly half the patients with DCM had increased T lymphocyte density and immune activation of endothelial and interstitial cells in their cardiac biopsies. A chronic autoimmune process is still active within the myocardium in a significant percentage of patients with DCM. Immunohistochemical analysis of cardiac biopsies will enhance the sensitivity of cardiac biopsy and is essential for the diagnosis of myocarditis.
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