Description
The erythema migrans rash is classically 5 to 6.8 cm in diameter, appearing as an annular homogenous erythema (59%), central erythema (30%), central clearing (9%), or central purpura (2%). Because of the "bullseye" description to describe the Lyme disease rash, the condition commonly called ringworm is sometimes confused with Lyme disease. Uncommonly, EM may be less than 5 cm in diameter. Multiple painless EM rashes may occur, indicating disseminated infection.
The EM rash occurs, according to sources, in 80% to 90% of those infected with Borrelia. A systematic review of the medical literature showed 80% of patients have an expanding EM rash, at the site of the tick bite, although some patients with EM do not recall a tick bite. In endemic areas of the United States, homogeneously red rashes are more frequent.
A significant group of practitioners disputes the generally accepted incidence of the rash, claiming it occurs in less than 50% of infections. These practitioners suggest a condition they call "chronic Lyme" (resembling chronic fatigue syndrome or fibromyalgia) exists in the absence of evidence for Borrelia infection. Their proposed treatment of patients with months or years of antibiotics is opposed by the wider medical community's scientific consensus, since these treatments are potentially dangerous, are not based on diagnoses with objective evidence, and have been shown in clinical trials to be ineffective even when evidence of infection is present.
Read more about this topic: Erythema Chronicum Migrans
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