Rethinking erythema migrans after 50 years of Lyme disease in the United States

Lyme disease is due to infection from the spirochete Borrelia burgdorferi, transmitted by blacklegged (genus Ixodes) ticks that yearly affects almost 500,000 Americans, with an expanding geographic range. Since over 80% of patients develop erythema migrans (EM), it is critical that these lesions be identified, as treatment effectively prevents systemic complications. Although many clinicians rely on a history of a tick bite and the buzzword “bullseye” lesion to diagnose EM, most patients do not recall a tick bite nor present with such a cutaneous “bull’s eye” appearance. A uniform oval erythematous patch is the most common finding, typically oriented along skin tension lines due to Borrelia interaction with dermal collagen. Nearly 20% of patients present with multiple lesions reflecting early spirochetal dissemination, with a resulting clinical appearance that places it in the differential diagnosis of “Christmas tree” eruptions. Vesiculobullous lesions and a darker purpuric or necrotic center can be seen in solitary lesions. EM-like lesions can also be seen in southern tick-associated rash illness. Vigilance in the detection of EM is essential in darker skin tones, as these individuals more frequently present with later stages of Lyme, suggesting earlier lesions were not properly diagnosed.