How is erythema migrans (EM) characterized in Lyme disease?

Shone

Vindhuja

@shone Early localized Lyme disease refers to isolated erythema migrans and to an undifferentiated febrile illness. This stage occurs 1-30 days after the tick bite.

Erythema migrans, the characteristic skin rash of Lyme disease, occurs in two thirds of patients with Lyme disease and develops at an average of 7 days after the tick bite. [4] The rash typically occurs at or near the site of the tick bite, which may be an area not normally visualized by individuals, such as the axilla, groin, or popliteal areas. It may be asymptomatic or it may itch or burn.

The rash typically expands over days and is not evanescent. It may not be observed until it is already full size. Clearing of portions of the rash as it expands may result in concentric rings of erythema, producing the classic bull’s-eye rash (see the image below). In the United States, however, erythema migrans is more likely to have a uniform color.
Although many patients present with erythema migrans, others first present with extracutaneous symptoms. In those cases, erythema migrans may have never occurred or may not have been recognized by the patient or correctly diagnosed by the physician.

Untreated, the rash may persist for 2-3 weeks. Eighty percent of patients with Lyme disease have only one episode of erythema migrans, whereas 20% may have recurrent episodes. Multiple lesions may occur in 20% of patients with Lyme disease; they result from hematogenous dissemination and are not the result of multiple tick bites