Lyme-folt: Tények és tévhitek

Lyme rash: Facts and misconceptions

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When does Erythema migrans, the circularly spreading redness on the skin — a bull’s-eye–like rash — appear?

Definition:

Erythema migrans. A circularly spreading redness on the skin, a bull’s-eye–like rash — also known as the Lyme rash. It is one of the most reliable signs of Lyme borreliosis infection.

Although not every person with Lyme disease develops erythema migrans, recognizing it is an important part of early diagnosis and treatment. However, it is important to note that erythema migrans does not always appear! Research shows that it occurs in only 30–50% of cases, and it may appear not only at the site of the tick bite but also elsewhere on the skin. According to a CDC study on Lyme carditis, only 42% of patients examined showed erythema migrans. Surveys conducted in the United Kingdom found that one-third of Lyme disease patients did not notice any rash. In cases where erythema migrans does appear, it should immediately raise suspicion, and a proper — preferably direct — test should be performed.

A skin lesion appearing 1–3 weeks after a tick bite, most often developing at the site of the bite. It is a concentrically expanding red area whose central part clears up over time, hence the term “bull’s-eye–like spot.” An important characteristic is that it never rises above the surface of the skin.

The shape of erythema migrans is not necessarily circular — it can also be oval or elongated — but even then, a tick bite should be suspected. The redness can reach up to 40 cm in diameter and may have diffuse, indistinct borders. It is also possible for more than one erythema migrans lesion to appear on the body.

The Lyme rash may not only appear but can also disappear from the body within a few days. However, this does not mean that the pathogen has left the body — the infection may still persist. The fastest and most accurate way to confirm this is through a direct test. Therefore, the goal of treatment is not merely to eliminate the redness, but to remove the infection itself — that is, the pathogen responsible for it.

It is important to remain alert even when erythema migrans is not perfectly red but rather reddish or blue-red in color, and not always circular — it may also appear oval. A characteristic feature of the skin lesion is that it increases in size over several days; in some cases, blisters may form in the center of the spot, although this occurs less frequently.

In the presence of early signs of infection, such as the appearance of the Lyme rash, DualDur is the most suitable laboratory test. This is because the development of a full, measurable immune response may take several weeks, making serological or immunological tests such as ELISA, Western blot, Immunoblot, or ELISpot unsuitable for early laboratory diagnosis. Meanwhile, the infection can reach various organs within a few days, and the number of bacteria can quickly reach its peak. Therefore, a direct blood test like DualDur can provide complete certainty and document the stage of infection before treatment begins.

Among serological tests, the Bózsik Western blot is capable of distinguishing the immune response to a possible previous infection from the one that develops later in response to a recent infection. By comparing the results of an immediate test with those of a follow-up test performed at a later time and after treatment, it provides valuable information for your physician.