Recognition and Treatment of Erythema Migrans: Are We Off Target?

• Erythema migrans
• Lyme disease
• Antibiotics
• Diagnosis
• Outcome and process assessment (health care)

The clinical manifestation most closely associated with Lyme disease is the rash that develops at the site of a bite from an Ixodes scapularis tick. Erythema migrans is present in at least 90% of objective cases of Lyme disease (1). Although it usually resolves spontaneously (that is, without any antimicrobial therapy), it may be the forerunner, in untreated patients, of cardiac, neurologic, or arthritic conditions, causing significant morbidity (1, 2). These sequelae generally respond to antibiotics (1-3). However, treatment of patients with erythema migrans is usually highly effective in preventing the development of these complications (1-3).

Despite the importance of erythema migrans, its clinical diagnosis has not been completely straightforward. Although once considered pathognomonic for Lyme disease, erythema migrans may be confused with other rashes that are virtually identical in appearance. These include a localized inflammatory reaction that may follow an arthropod bite but is unassociated with Borrelia burgdorferi infection (4, 5), and a recently described rash linked to the bite of an Amblyomma tick and a separate etiologic agent (6). In practice, erythema migrans has been diagnosed primarily on clinical grounds, without laboratory testing. However, microbiological confirmation is useful in a research setting to distinguish definite cases of Lyme disease and to define the true clinical features (7, 8). Recovery of B. burgdorferi from cultures of skin biopsy specimens or blood is the gold standard for diagnosis of early Lyme disease.

In this issue, Smith and colleagues (9) describe the clinical manifestations of illness and outcome in a group of U.S. patients with erythema migrans and laboratory evidence of B. burgdorferi infection. All patients were part of a larger cohort of nearly …