What Is This Annular Rash?

THE CASE: The mother of a 4-year-old boy noticed a rash on her son's left shoulder the day before. The otherwise healthy, asymptomatic boy plays outdoors daily in his hometown of West Virginia. Earlier in the week, he told his mother that he had felt a "scab" on his shoulder and had picked it off.

Answer on Next Page

Erythema chronicum migrans is the correct answer.

The "scab" the child picked off his skin was probably a tick. The shoulder rash represented early localized infection with the spirochete Borrelia burgdorferi, which manifests as erythema chronicum migrans (ECM), an expanding, erythematous, annular rash that sometimes exhibits complete or partial central clearing. The lesion typically increases to 5 cm or more in diameter.

Lyme disease was diagnosed. This tick-borne illness is transmitted by 2 species of deer tick-Ixodes scapularis in the East and Midwest and Ixodes pacificus in the West. Lyme disease is considered endemic to New England, areas of California, the Mid-Atlantic, and the Great Lakes region.¹ Although it is not considered endemic in West Virginia, 30 to 60 new cases are reported there yearly.² Also, this child resided in the northern part of the state near the border of Pennsylvania.

The classic ECM ("bull's-eye") rash of early localized Lyme disease may be associated with constitutional symptoms, such as fever, chills, myalgias, and malaise. The rash appears between 1 and 32 days (a median of 11 days) after the tick bite.³ Early disseminated infection occurs within a few days to weeks and can be characterized by multiple reddish annular lesions, migratory joint pain, facial nerve paralysis, meningitis, and carditis.^1,4 Late disseminated infection (persistent Lyme disease) occurs weeks to months after untreated infection and includes arthritis, encephalopathy, and chronic polyneuropathy.^1,4

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Diagnosis is made clinically on the basis of symptoms and travel to or residence in an area in which Lyme disease is endemic. Serological testing may be needed for diagnosis in later stages of the disease. A 2-step approach with a sensitive enzyme immunoassay or immunofluorescent antibody assay followed by confirmation with a positive or equivocal Western blot analysis result is recommended.

Tinea corporis is in the differential diagnosis; however, the acute onset and clinical presentation with potential tick exposure rule out this superficial fungal infection. Nummular eczema, associated with pruritic coin-shaped papules and plaques with vesicles, is also unlikely because of its acute presentation. Hansen disease, or leprosy, a rare chronic infection caused by Mycobacterium leprae, is another consideration. It is characterized by scaling violaceous plaques and loss of sensation along the peripheral nerves. However, the clinical presentation and the patient's lack of exposure and travel eliminate this as the diagnosis.

Treatment of Lyme disease in nonpregnant patients 8 years and older is doxycycline; amoxicillin is the treatment of choice in children younger than 8 years.^3,5 Duration of antibiotic treatment ranges from 14 to 28 days depending on the extent of disease.³

Case and photograph courtesy of Jane E. Holt, DO, Stacey M. Humphreys, MD, and Linda S. Nield, MD, of West Virginia University School of Medicine in Morgantown.

References:

REFERENCES:1. Bratton RL, Whiteside JW, Hovan MJ, et al. Diagnosis and treatment of Lyme disease. Mayo Clin Proc. 2008;83:566-571.
2. Centers for Disease Control and Prevention (CDC). Lyme disease-United States, 2003-2005. MMWR. 2007;56:573-576.
3. American Academy of Pediatrics. Lyme disease. In: Pickering LK, Baker CJ, Kimberlin DW, Long SS, eds. Red Book: 2009 Report of the Committee on Infectious Diseases. 28th ed. Elk Grove Village, IL: American Academy of Pediatrics. 2009:430-435.
4. Nau R, Christen HJ, Eiffert H. Lyme disease-current state of knowledge. Dtsch Arztebl Int. 2009;106:72-82. doi:10.3238/arztebl.2009.0072.
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 [published correction appears in Clin Infect Dis. 2007;45:941]. Clin Infect Dis. 2006;43:1089-1134.