Erythema migrans

Lyme disease

"Erythema migrans is the only manifestation of Lyme disease in the United States that is sufficiently distinctive to allow clinical diagnosis in the absence of laboratory confirmation." Often, but not always, mentions of a target lesion (bull's-eye lesion) are talking about erythema migrans. However, the appearance of erythema migrans can vary considerably: while some look like a bull's eye, in the U.S. most are evenly red or bluish, without a central or ring-like clearing. A minority of patients never have any rash. Because Lyme disease can within a few weeks cause long-term neurologic complications, persons with a rash and recent history of outdoor activities where Lyme is common should seek a doctor for diagnosis.

Presentation

The initial sign of about 80% of Lyme infections is an erythema migrans (EM) rash at the site of a tick bite, often near skin folds, such as the armpit, groin, or back of knee, on the trunk, under clothing straps, or in children's hair, ear, or neck. Most people who get infected do not remember seeing a tick or the bite. The EM rash appears typically one or two weeks (range 3–32 days) after the bite. The most distinctive features of the EM rash are the speed and extent to which it expands, respectively 2–3 cm per day and up to a diameter of 5–70 cm (50% attain more than 16 cm). The rash is usually circular or oval, red or bluish, and may have an elevated or darker center. In about 79% of cases in Europe but only 19% of cases in endemic areas of the U.S., the rash gradually clears from the center toward the edges, possibly forming a "bull's eye" pattern. The rash may feel warm but usually is not itchy, is rarely tender or painful, and takes up to four weeks to resolve if untreated.

The EM rash is often accompanied by symptoms of a viral-like illness, including fatigue, headache, body aches, fever, and chills, but usually not nausea or upper-respiratory problems. These symptoms may also appear without a rash, or linger after the rash disappears. Lyme can progress to later stages without these symptoms or a rash.

A person with an asymptomatic EM rash can easily miss its significance. However, if the initial EM rash is not treated, the infection can disseminate through the lymphatic system or blood. Within days or weeks, additional EM rashes, usually smaller, can appear at other sites, or the infection can cause more serious complications in the nervous system, heart, or joints.