Erythema migrans is the characteristic physical finding of early Lyme disease. It begins as a red macule at the site of the Ixodes tick bite. Classically, the macule expands with central clearing, as in this image, but in many patients, no central clearing occurs. Some patients have central erythema surrounded by a pale ring, and a few develop vesicular or ulcerated centers.
Image courtesy of Thomas Habif, MD.