Immunohistochemistry in dilated cardiomyopathy

The aetiology of dilated cardiomyopathy is unknown by definition. Viral myocarditis is often viewed as an early stage in the progression of the disease leading to cardiomyopathy and heart failure in humans. The chronic inflammatory process is manifested histologically as a sparse, diffuse lymphocytic infiltration of the myocardium, classified as borderline or ongoing myocarditis according to the Dallas classification. Because of limitations of light microscopy, chronic myocarditis remains an enigmatic condition to diagnose and to treat. In contrast to routine histological staining procedures, immunohistochemical methods enable better identification and quantification of infiltrating cells and also provide further evidence that the activated immunological process within the myocardium is ongoing. In 176 patients with clinically suspected dilated cardiomyopathy, borderline myocarditis was diagnosed in only 14 cases (8%) histologically. However, using immunohistological analysis of endomyocardial biopsies, pathologically increased lymphocytic infiltration was revealed in 67 biopsy specimens (38%), and activated lymphocytes or activated macrophages in all analysed inflamed cardiac tissues. All positive biopsies showed an activated vascular endothelium, demonstrated by the enhanced expression of different adhesion molecules. Various cytokines were locally released from activated inflammatory cells. This may cause a cytokine-rich micro-environment which could be responsible for the enhanced expression of adhesion molecules and thereby contribute to the inflammatory traffic of immune cells into inflamed myocardial areas. These observations underline the hypothesis that the immune process is still active in a group of patients with clinically suspected dilated cardiomyopathy, causing progression of the disease.