[Lyme's disease, a possible cause of isolated acute myocarditis].

The frequency of cardiac lesion in patients with other signs of Lyme disease has been estimated at 8 percent. The usual manifestation of myocardial involvement is a varying degree of atrioventricular block or more diffuse signs of myocarditis. Autopsy or intramyocardial biopsy provides a histological diagnosis of myocarditis. Microscopy shows a diffuse lympho-plasmocytic infiltrate with presence of macrophages in the myocardium, associated with a varying number of necrotic myocytes. Structures resembling spirochetes have been found in some cases. Exceptionally, the cardiac lesion may be isolated, presenting as an acute atrioventricular block and/or an acute myocarditis; in such cases the diagnosis of cardiac lesion caused by Lyme disease is made on serological grounds. We report the case of a 30-year old man admitted for acute myocarditis which turned out to be totally regressive. Intramyocardial biopsy showed interstitial congestion associated with inflammatory lympho-histiocytic infiltrates and eosinophilic polymorphonuclears; the myocardial fibres in contact with these infiltrates appeared to be altered. The diagnosis of Lyme disease was subsequently confirmed by serological tests. Patients with myocarditis caused by Lyme disease must be treated with antibiotics. Recent reports have demonstrated the presence of spirochetes in the myocardium of patients with dilated cardiomyopathy, suggesting that the spirochete Borrelia burgdorferi might be associated with, or play a part in, the subsequent occurrence of dilated cardiomyopathy.