A red annular "bull's eye" patch, known as erythema migrans (EM), is the most common presentation of early Lyme disease
Lyme disease can be difficult to diagnose, experts say, because at least 40 percent of sufferers don't present with the characteristic "bull's-eye" rash, and about a fifth of patients don't exhibit skin lesions.
A red annular "bull's eye" patch, known as erythema migrans (EM), is the most common presentation of early Lyme disease.
In Europe, B. afzelii, B. garinii, B. burgdorferi and, occasionally, other species of Borrelia cause Lyme disease, according to a review by Feder et al in the Oct. 4, 2007, New England Journal of Medicine.
Some - but by no means all - people bitten by infected ticks will notice or remember the telltale rash. Experts disagree on the percentage of people who have skin manifestations of the disease.
"Health department statistics from various states indicate that only 35 percent to 60 percent of Lyme patients ever see an EM rash. Sometimes the rash is hidden under hair on the scalp or in places where it is not noticed, especially in children," says Raphael Stricker, M.D., specialist in internal medicine, San Francisco, and past president of the International Lyme and Associated Diseases Society.
About 20 percent of Lyme cases do not exhibit skin lesions, says Col. Joe Pierson, M.D., dermatology consultant for the U.S. Army Surgeon General; assistant professor of dermatology, Uniformed Services University, Bethesda, Md.; and dermatologist, U.S. Military Academy, West Point, N.Y.
Many patients also have systemic signs or symptoms, such as fatigue, myalgias, arthralgias, headache, fever/chills and regional lymphadenopathy, he says.
EM lesions expand centrifugally and tend to orient along Langer's lines of the skin, according to Dr. Pierson.
EM is a sign that the disease is still active, according to Dr. Stricker.
"EM is usually asymptomatic, though mild itching or burning pain may be present. The location of the nonscaling EM patch is often at the popliteal fossa, groin and axilla, or regions where clothing disrupts a tick's journey, such as a beltline or bra strap," Dr. Pierson says.
"The trunk is commonly involved in children, while leg lesions are relatively more common in adults."
For definitive clinical diagnosis, the EM should be 5 cm in its largest diameter. The lesion typically appears approximately one to two weeks after a tick bite, though the range can be anywhere from three to 30 days, and a central punctum where the bite occurred may be noted, according to Dr. Pierson.
Skin manifestations of Lyme vary from patient to patient.
Central clearing of EM lesions is actually absent in the majority of patients who have Lyme disease in North America. Commonly, patches are uniform in color, although dermatologists might note central darkness, according to Dr. Pierson.