A child presents with an erythema migrans rash and a history suggestive of tick exposure. What is the most important first question to determine the diagnosis?

A child presents with an erythema migrans rash and a history suggestive of tick exposure. What is the most important first question to determine the diagnosis?

• A. Ask about recent tick bites
• B. Obtain a skin culture
• C. Order blood cultures
• D. Perform serologic testing

Answer: (A)

The most important thing to establish first is whether there has been recent tick exposure. The presence of an erythema migrans rash in a child who has had contact with ticks in a Lyme-endemic area makes early Lyme disease a highly likely diagnosis, and this is a clinical diagnosis that relies on exposure history as the key initial clue. Serology and cultures are not reliable for early Lyme disease: antibodies may not be present yet, and cultures from skin or blood are not routinely informative in the early localized stage. So asking about recent tick bites directly links the rash to a plausible cause and helps justify prompt management.

The most important thing to establish first is whether there has been recent tick exposure. The presence of an erythema migrans rash in a child who has had contact with ticks in a Lyme-endemic area makes early Lyme disease a highly likely diagnosis, and this is a clinical diagnosis that relies on exposure history as the key initial clue. Serology and cultures are not reliable for early Lyme disease: antibodies may not be present yet, and cultures from skin or blood are not routinely informative in the early localized stage. So asking about recent tick bites directly links the rash to a plausible cause and helps justify prompt management.