Bury the Buzzword: Bull’s-Eye Rash

The buzzword “bull’s-eye rash” is used to describe the appearance of a rash located on the skin. The rash has either a cleared area or red area in the center, with red rings circling it. It can also be known as a “target-rash.”

I came across four main conditions that cause a bull’s-eye rash. They are Lyme disease, Southern Tick Associated Rash Illness (STARI), erythema multiforme, and erythema annulare centrifugum (EAC).

Lyme disease is the most well-known condition that causes a bull’s-eye rash. The rash is also known as erythema chronicum migrans (ECM or EM). It appears early in the infection, and is formed around the area where the tick bit the skin. This is the first condition you should think about ruling out when you see this rash. You should ask about any history of exposure to the woods, such as hiking or camping, and if the patient has noticed any ticks on them. The rash is most commonly found in the groin, armpit, and thigh.

Southern Tick Associated Rash Illness (STARI) can cause a rash that looks identical to that of Lyme disease, but is not caused by Borrelia burgdorferi. This condition is also known as Masters disease. It is postulated that the bacteria Borrelia lonestari from the bite of the lone star tick, Amblyomma americanum may cause the disease. This tick is only present in the south and northeast. Patients may present similar to those with Lyme disease, except that their rash might be of lesser size.

Erythema multiforme can cause a bull’s-eye rash because of a hypersensitivity reaction or infection. The most common causes are herpes simplex virus or mycoplasma bacteria. The hypersensitivity reaction can be caused by certain drugs such as antibiotics or seizure mediations. It can even progress to Stevens-Johnson syndrome.

Erythema annulare centrifugum (EAC) can also cause a bull’s-eye rash because of a hypersensitivity reaction. The hypersensitivity reaction can be caused by infection, drugs, chemical exposure, autoimmune diseases, or cancer. It can be considered a chronic form of erythema multiforme that is most commonly located on the legs.

The “bull’s-eye rash” could easily be another image question that shows up on the boards. You will most commonly be tested over Lyme disease, but you should add these other three conditions to your differential if you are able. Even if you are not tested over these on the boards, it is good to have more than one thing come to mind when you see an actual patient present with a bull’s-eye rash.

Sources:

"Erythema Annulare Centrifugum." The Free Dictionary Medical Dictionary. Farlex. Web. 19 Dec. 2011. <http://medical-dictionary.thefreedictionary.com/erythema+annulare+centrifugum>.

Fauci, Anthony S., and Tinsley Randolph Harrison. "Lyme Borreliosis." Harrison's Principles of Internal Medicine. 17th ed. New York: McGraw-Hill Medical, 2008. Print.

Goljan, Edward F. "Musculoskeletal and Soft Tissue Disorders." Rapid Review Pathology. Ed. Edward F. Goljan. 3rd ed. Philadelphia, PA: Mosby/Elsevier, 2010. 531. Print.

"Southern Tick Associated Rash Illness (STARI)." ALDF.com. American Lyme Disease Foundation, 28 Apr. 2011. Web. 19 Dec. 2011. <http://www.aldf.com/stari.shtml>.

Vorvick, Linda J., Kevin Berman, and David Zieve. "Erythema Multiforme." NIH.gov. PubMed Health, 10 Oct. 2010. Web. 19 Dec. 2011. <http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001854/>.

Willard, Robert J. "Erythema Annulare Centrifugum." Emedicine.medscape.com. Ed. Dirk M. Elston. WebMD, 12 July 2010. Web. 19 Dec. 2011. <http://emedicine.medscape.com/article/1122701-overview>.