An update on the diagnosis and treatment of early Lyme disease: "focusing on the bull's eye, you may miss the mark".

To confidently diagnose and treat Lyme disease, the clinician must first understand the natural history of this disease, especially its protean early manifestations. Emergency physicians, primary care physicians, and other providers need to be vigilant in terms of the timely recognition of erythema migrans (EM), the unique marker of early localized stage 1 disease. The classic EM, originally described as a slowly expanding bull's eye lesion, is now recognized to be present in only the minority of cases (9%); the dominant morphologic lesion of EM is now recognized to be the diffusely homogenous red plaque or patch, which occurs in over 50% of cases. This update will define the current morphologic features of early Lyme disease, the indication for serologic studies, and the most recent treatment guidelines, including therapeutic pitfalls.