Background: Cardiac involvement in Lyme disease is uncommon and typically manifests clinically by conduction disturbances. Postmortem identification of Borrelia burgdorferi has never been reported in a case of Lyme carditis.
Methods and results: We describe the case of a 37-year-old Caucasian man with a 1-month history of fevers, rash, and malaise who died unexpectedly on the day after he underwent medical evaluation. The only clinical cardiac abnormality found was that of second-degree atrioventricular block. At autopsy, a diffuse carditis, characterized by infiltrates of macrophages, lymphocytes, and eosinophils and primarily in an interstitial, endocardial, and perivascular distribution, was found. Serologic testing from blood drawn on the day before his death demonstrated IgG and IgM antibodies against B. burgdorferi, confirmed by Western blot. Postmortem polymerase chain reaction (PCR) performed in myocardial tissue amplified B. burgdorferi DNA encoding outer-surface protein A.
Conclusions: Lyme carditis should be considered in the differential diagnosis of interstitial myocarditis with mixed inflammatory infiltrates. This diagnosis can be confirmed by PCR testing.