Background: Organ- and disease-specific cardiac autoantibodies, detected by indirect immunofluorescence, represent markers of autoimmunity in a subgroup (25-35%) of patients with dilated cardiomyopathy or myocarditis from Northern Europe and the United States of America. Autoantibody frequencies, as well as associations between clinical and immunological features, may vary in patients from different countries, due to ethnically related differences in genetic susceptibility to autoimmune disease.
Methods: We assessed the frequency of cardiac autoantibodies in a series from Italy, including 91 subjects with idiopathic dilated cardiomyopathy (61 male, aged 49 +/- 11 years) and 11 with biopsy-proven (Dallas criteria) myocarditis (7 male, aged 23 +/- 16), including 2 cases of giant cell myocarditis. Controls were 160 patients with other cardiac disease, 141 with ischemic heart failure and 270 normals Cardiac antibody test was performed blindly by indirect immunofluorescence on normal human myocardium and skeletal muscle.
Results: The frequency of organ-specific cardiac autoantibodies was higher (p = 0.0001) in myocarditis (45%) and in dilated cardiomyopathy (20%) than in other cardiac disease (1%), in ischemic heart failure (1%), or in normals (2.5%). Cross-reactive antibodies were detected in similar proportions of study patients and controls. Both patients with giant cell myocarditis were antibody positive. Myocarditis patients with cardiac antibodies had shorter duration of symptoms compared to those who were antibody negative (0.4 +/- 0.3 vs 4 +/- 1 months, p = 0.004). In dilated cardiomyopathy, antibody status was not associated with any clinical or diagnostic feature.
Conclusions: Autoimmunity is involved in a subset of patients with myocarditis and with dilated cardiomyopathy, regardless of their geographical origin or immunogenetic background. The antibody frequency in our dilated cardiomyopathy series from Italy tended to be lower than in other countries. This may reflect reduced antibody levels with disease progression and/or the recognised feature that Mediterranean populations are often less susceptible to autoimmune disease.