Primary and secondary erythema migrans in central Wisconsin

We report a series of 28 consecutive patients with erythema migrans (EM) who underwent skin biopsies for culture of Borrelia burgdorferi. Culture results, Lyme serologic findings, and clinical features in patients with only primary EM are compared with those in patients with secondary EM.

Culture preparations of skin specimens obtained from six of 12 patients with only primary EM, and from 14 of 16 patients with secondary EM were positive for B burgdorferi. Seven patients with only primary EM were initially seronegative, and only one patient had an annular lesion. A central crusted punctum was present in five of six primary EM lesions that were not culture positive, but in none of nine culture-positive primary EM lesions. Patients with secondary EM were all seropositive and had less cutaneous and more constitutional symptoms than patients with only primary EM. Three patients with secondary EM had abnormal liver enzyme profiles, one patient had complete heart block, and one patient had myocarditis simulating infarction. Less than one third of all patients recalled a tick bite. An isomorphic nonresponse was seen in skin previously involved with secondary EM in one patient who had a drug exanthem from amoxicillin.

Borrelia burgdorferi can be reliably cultured from skin biopsy specimens of secondary EM. Culture preparation aids definitive diagnosis of Lyme disease in patients with only primary EM who often lack constitutional symptoms, have nondiagnostic lesions, or are seronegative.