Which statement about erythema migrans and Lyme disease is true?

Which statement about erythema migrans and Lyme disease is true?

• A. Serologic testing is required.
• B. Erythema migrans rash is diagnostic of Lyme disease and no further testing is necessary.
• C. Erythema migrans rash must be confirmed with skin culture.
• D. Erythema migrans rash is always accompanied by fever.

Answer: (B)

Erythema migrans is the classic early sign of Lyme disease, and in an area where Lyme is common, its appearance is enough to establish the diagnosis without lab confirmation. The rash is highly characteristic and reflects infection with Borrelia burgdorferi, so treatment should begin based on the clinical finding alone. Antibody tests aren’t reliable early in the illness because the immune response takes time, so a negative serology doesn’t rule out Lyme disease when EM is present. Skin culture isn’t used to confirm EM because it’s impractical and rarely helpful, and fever isn’t universal—many children with EM do not have fever. That combination of factors makes the statement that erythema migrans rash is diagnostic and no further testing is necessary the best choice. If EM isn’t present or testing is needed later, serology becomes more informative.

Erythema migrans is the classic early sign of Lyme disease, and in an area where Lyme is common, its appearance is enough to establish the diagnosis without lab confirmation. The rash is highly characteristic and reflects infection with Borrelia burgdorferi, so treatment should begin based on the clinical finding alone. Antibody tests aren’t reliable early in the illness because the immune response takes time, so a negative serology doesn’t rule out Lyme disease when EM is present. Skin culture isn’t used to confirm EM because it’s impractical and rarely helpful, and fever isn’t universal—many children with EM do not have fever. That combination of factors makes the statement that erythema migrans rash is diagnostic and no further testing is necessary the best choice. If EM isn’t present or testing is needed later, serology becomes more informative.