The most common clinical manifestation of Lyme disease is the rash, erythema migrans, formerly called erythema chronicum migrans (Figs. 6-9). The rash typically occurs 7-10 days after the tick bite and is present in 60-80 percent of patients with Lyme disease. Because over half of the patients with Lyme disease do not remember a tick bite, absence of a history of a tick bite does not exclude the diagnosis. The rash typically has an erythematous annular border that gradually expands and has partial central clearing (Fig. 6, 7). The rash can occur anywhere on the body, is typically warm to the touch, and is occasionally pruritic. The median diameter of the rash is 15 cm. Over time the central portion of the rash may become necrotic or vesicular (Fig. 8). The rash usually resolves within 3 to 4 weeks; if antibiotic treatment is given, the rash usually fades by 1 week. Borrelia burgdorferi has been isolated from the outer rim of the skin lesion at this stage. During this patients may also have flu-like symptoms, regional lymphadenopathy, and other non-specific complaints.