Trunk rashes with central clearing

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Trunk rashes with central clearing
Trunk rashes with central clearing

CASE #2: Erythema migrans

Histopathologic finding of a dermal hypersensitivity reaction, along with the characteristic clinical appearance, confirmed the diagnosis of erythema migrans (EM).

Introduced in 1909, EM was described as an expanding ring-like lesion and thought to be the result of a bite of an Ixodes (deer) tick. Studies have correlated the rash of EM with early, localized Lyme disease, which is a systemic infection with the spirochete Borrelia burgdorferi.

Lyme disease is transmitted via an infected tick's salivary glands to the individual at the site of the inoculation. From there, the spirochete can either be eliminated by the host's immune system, remain localized at the site of the bite, or spread to surrounding and distant tissue.

EM is often referred to as the "bull's-eye rash" because of its clinical appearance. The rash typically starts as a red inflammatory papule that expands in a circular or oval shape over several days or weeks to an average size of 16 cm. Central clearing occurs simultaneously. At times, the primary papule or proximal redness remains, contributing to the "bulls-eye" or "target" appearance.

Several similar lesions can erupt elsewhere on the body. Although the lesions are usually macular, papular and scaly variations exist. The rash may be asymptomatic or cause mild itching or burning. Up to 50% of patients describe such mild flulike symptoms as malaise, poor appetite, and myalgia.

EM typically appears at the site of the tick bite but may start anywhere else on the body. The rash can appear one day to one month after a tick bite, with an average onset of seven to 14 days post-bite. EM typically persists for two to four weeks, and in some patients it recurs intermittently if left untreated. Unfortunately, many patients may have no evidence of the rash, and Lyme disease only presents in the later stages with extracutaneous manifestations.

Symptoms of Lyme disease result from both infection with the spirochete and from the body's immune responses to the infection. The multiple lesions of EM, when present, are most likely the results of the body's immune response.

Clinical manifestations are generally divided into three groups: early localized, early disseminated and chronic disseminated. EM is the primary manifestation of early-localized disease. (A detailed description of the symptoms of and treatment for disseminated disease is lengthy and beyond the scope of this article.)

While the classic appearance of the rash will assist in the diagnosis, it is important to consider the epidemiological context (i.e., geography, season and history of outdoor exposure). Further workup and monitoring is only indicated for those who exhibit extracutaneous manifestations and those who do not show prompt resolution of the rash with recommended treatment.

For the latter group, consider such alternative diagnoses as cellulitis or contact dermatitis, as well as co-infection with such other tick-borne illnesses as relapsing fever, tularemia, babesiosis, Rocky Mountain spotted fever and Colorado tick fever.4 Individuals presenting with an inflammatory erythematous papule at the inoculation site that appeared while the tick was still attached or within hours of the bite most likely do not have EM, but rather are showing a hypersensitivity reaction to the tick.

Patients presenting with EM and a positive history of exposure to a tick-infested area do not need serologic testing for a diagnosis of Lyme disease, and antibiotic therapy should be initiated. Empiric antibiotic therapy is also reasonable, even if the clinical diagnosis of EM is moderately probable and not certain. For other Lyme disease symptoms, such laboratory studies as B. burgdorferi antibody titers are necessary. Testing early in the course of Lyme disease is often still negative and may cause a dangerous delay in treatment.

EM generally responds and improves within a few days of starting antibiotic therapy. Controversy exists regarding optimum duration of treatment, with recommendations ranging from 10 to 30 days. Doxycycline 100 mg b.i.d. is the preferred drug for oral treatment in nonpregnant adults and children older than age 8 years. Amoxicillin 500 mg t.i.d. is the drug of choice for pregnant and pediatric patients.

Second-line drugs include erythromycin, azithromycin (Zithromax, Zmax), and cefuroxime (Ceftin) and are reserved for patient intolerant of first-line agents. With appropriate treatment, the prognosis for EM is excellent.

Early removal of ticks will lower the risk of contracting Lyme disease. Ticks need to be attached for at least 24 hours before disease transmission can occur. Individuals presenting with ticks that are not engorged do not need any treatment. Prophylactic treatment with a single dose of doxycycline 200 mg for nonpregnant adults and children older than age 8 years is recommended for such cases. Removal of the tick should be done carefully, using tweezers to grasp the tick close to the skin and pulling gently outward to detach.

Patients with EM should be educated regarding disease transmission as well as prevention strategies to avoid a repeat episode (e.g., cover exposed skin and tuck pants into the shoes when walking in wooded, brushy or grassy areas). Applying insect repellants containing DEET (N,N- diethyl-m-toluamide) will help repel ticks, however the American Academy of Pediatrics advises that children should not be exposed to products with greater than 10% concentration of DEET. Wearing light colored clothing will aid in identifying lingering insects. It is imperative to inspect the entire skin for evidence of ticks immediately after returning from outdoor exposures,5 paying special attention to body folds and the scalp. When a tick initially attaches to the human skin, it may be as small as a pinhead and difficult to see without a careful inspection. As the tick remains attached and feeds, it will become more engorged and more noticeable but may have already introduced infection by this time.

This patient was treated with doxycycline 100 mg b.i.d. for 14 days and reported resolution of the rash one week later. 

Esther Stern, NP-C, is a family nurse practitioner at Advanced Dermatology & Skin Surgery, P.C., in Lakewood, N.J.


1. Bressler GS, Jones RE Jr. "Erythema annulare centrifugum." J Am Acad Dermatol. 1981;4:597-602.

2. Weyers W, Diaz-Cascajo C, Weyers I. "Erythema annulare centrifugum: results of a clinicopathologic study of 73 patients." Am J Dermatopathol. 2003;25:451-462.

3. Kim KJ, Chang SE, Choi JH et al. "Clinicopathologic analysis of 66 cases of erythema annulare centrifugum." J Dermatol. 2002;29:61-67.

4. McGinley-Smith DE, Tsao SS. "Dermatoses from ticks." J Am Acad Dermatol. 2003;49:363-392.

5. Wormser GP, Dattwyler RJ, Shapiro ED et al. "The clinical assessment, treatment, and prevention of lyme disease, human granulocytic anaplasmosis and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America." Clin Infect Dis. 2006;43:1089-1134.

All electronic documents accessed April 5, 2012.

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