Erythema migrans

Erythema migrans (EM; previously known as erythema chronicum migrans [ECM]) is the most common objective manifestation of Lyme disease, accounting for about 90% of cases [1-4]. This rash is distinctive enough to have enabled early investigators to describe the clinical manifestations of Lyme disease years before the discovery of the causative pathogen, Borrelia burgdorferi, and the development of the first diagnostic laboratory assays. Recognition of the tick vector for Lyme disease was linked to the observation that EM arises within days to a few weeks at the exact site of the bite of certain Ixodes ticks [2,5-8].