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September 12, 2007

Diagnosis of Erythema Migrans

Author Affiliations

Letters Section Editor: Robert M. Golub, MD, Senior Editor.

JAMA. 2007;298(10):1159-1160. doi:10.1001/jama.298.10.1159-b

To the Editor: In their Rational Clinical Examination article, Drs Tibbles and Edlow1 reviewed the accuracy of history and physical examination findings for the diagnosis of erythema migrans. There are 2 issues that are important to consider.

First, Table 2 states that erythema migrans is accompanied by mild pain or itch. However, in most cases erythema migrans is entirely asymptomatic.2 Pruritus, when present, may be due to a hypersensitivity reaction to the tick bite, irrespective of the presence of borrelial pathogens.3 This pruritus lasts about a week, resolving around the time that most cases of erythema migrans begin to appear.2 Moreover, a study conducted in Rhode Island suggests that patients with significant pruritus after a tick bite are less likely to develop Lyme disease than those who experience mild or no itch.3 An explanation offered is that individuals with prominent itch at the bite site are more likely to be aware of the affected area, leading to early removal of the tick, thus preventing transmission of the pathogen. Also, the presence of an itchy hypersensitivity response indicates prior exposure to tick bites. Individuals with multiple previous tick bites may have acquired a protective immune response (perhaps to tick salivary antigens) that thwarts disease transmission.3

Second, the entry for granuloma annulare in Table 2 of the study may not be correct. This condition is almost never scaly; indeed, the presence of scale generally excludes the diagnosis of granuloma annulare.4 Thus, granuloma annular is even more similar to erythema migrans than the table suggests.

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Article Information

Financial Disclosures: None reported.

Disclaimer: The opinions expressed herein are those of the author and not those of the Department of Defense.

Tibbles CD, Edlow JA. Does this patient have erythema migrans?  JAMA. 2007;297(23):2617-262717579230Google ScholarCrossref
Edlow JA. Tick-borne diseases, Lyme [eMedicine Journal Web site]. eMedicine. January 3, 2007. http://www.emedicine.com/emerg/topic588.htm. Accessed June 28, 2007
Burke G, Wikel SK, Spielman A.  et al.  Hypersensitivity to ticks and Lyme disease risk.  Emerg Infect Dis. 2005;11(1):36-4115705320Google Scholar
Dahl MV. Granuloma annulare. In: Freedberg IM, Eisen AZ, Wolff K, Austen KF, Goldsmith LA, Katz S, eds. Fitzpatrick's Dermatology in General Medicine. 6th ed. New York, NY: McGraw Hill; 2003:980-984