Erythema migrans is a characteristic Lyme disease symptom thought to occur in around 70-90% of cases. The center of the rash appears either as a solid expanding red blotch, or a red spot surrounded by a ring of clear skin and an outer red ring, forming a ‘bull’s eye’ pattern. This bull’s eye skin rash is more prevalent with B. afzelii infections than other strains and, although all of the Borrelia strains associated with Lyme disease can cause this pathognomic symptom, some of those infected will not develop this initial, or secondary, rash.
Those infected with B. garinii, for example, may develop a non-annular (no central clearing) red blotch instead. Variation in Lyme disease symptoms also seem to occur between men and women, with evidence that erythema migrans arises more frequently in cases of B. afzelii infections in women than in men. The expanding rash usually radiates from the initial site of the tick-bite, with early disseminated Lyme disease often indicated by two or more examples of the bull’s eye rash at locations away from the site of the tick bite. The center of the rash usually becomes indurated (hardened) and is usually darker than the outer ring even in the absence of clearing in-between.
When Bull’s Eye Rash Appears
The appearance of erythema migrans can occur within 3-30 days of infection with the disease, with an average occurrence between 1-2 weeks after Lyme disease transmission. The rash is not usually itchy or painful, due to substances in the ticks’ saliva, but may be warm to the touch. A rash of this kind may be noticed by a patient’s partner first, especially when it occurs on the back, neck, or back of the legs. The erythema migrans rash is usually around 5-6 inches wide but can be smaller or larger, sometimes reaching more than a foot across and even covering the whole of a person’s back in some cases. Erythema migrans is commonly observed as it expands gradually over a period of days rather than occurring as an acute widespread swelling or reddening of the skin.
Characteristics of Bull’s Eye Rash
The rash is likely to be located in the armpit, groin, nape of the neck, or the back of the knee as these creases provide ticks with a favourable area to remain attached to the body without being noticed and brushed off. A number of tick bites can occur, leading to a crossover of rashes in some cases. Multiple rashes may also arise, even without an initial bull’s eye rash having occurred. The initial rash commonly lasts for around 3-5 weeks but may last only a day or so or not occur at all. Patients with darker skin may not notice the rash as it can be extremely hard to see, occurring as a dark, bruise-like mark on the skin rather than the high-contrast bull’s eye featured in many pictures of Lyme disease. In addition, those who were bitten during a holiday where they also acquired a tan may not notice the rash as both the tan and the rash may dissipate at the same rate.
The development of erythema migrans often coincides with other Lyme disease symptoms such as:
- Joint pain
The similarity between such symptoms and a mild cold or general fatigue following a robust hiking holiday or other outdoor activity can easily lead to the signs of Lyme disease being ignored. These flu-like symptoms of Lyme disease are usually only brief initially, but can then recur as part of a wider manifestation of the infection later on as the illness continues to develop. It is easy, therefore, to see how localized early stage Lyme disease symptoms can go unnoticed or unaddressed with patients not seeking medical attention for such seemingly simple ailments.