Bull’s-eye Rash: The Biggest Sign for Lyme Disease

Ticks are everywhere, and although some can be less harmful than others, all of them can be carriers of a bacterium that can cause a wide range of symptoms and a debilitating disease called Lyme.

Because these small creatures have become more active all year round, regular tick control becomes more essential. But for those who think they’ve been bitten by a tick, they might want to watch out for a bull’s-eye rash.

What’s the Bull’s-Eye Rash?

Also known as erythema migrans, the rash is the hallmark of Lyme disease, a condition caused by a bacterium present in ticks. It is a rash that occurs around the site of the tick bite.

The prominent appearance of erythema migrans is a central, red area with outwardly expanding rings of clear skin. It takes some time for this rash to develop. When it finally appears, it’s typically larger than 4 centimeters across or about the size of your hand or forearm.

Although not required for diagnosis, the classic bull’s-eye pattern is reported by approximately 70 percent of people who have Lyme disease. In some people, the rash of Lyme might be absent or barely visible.

A small percentage of people with early localized Lyme disease will not develop a rash. In about half of all cases, erythema migrans is not visible at the site where the tick has attached to the skin. This “delayed” development is due to several factors:

  • The location might be hidden (between toes or fingers).
    There might not be much immune reaction occurring at first.
    The patient might apply an antibiotic cream after removing the tick.
    There might be so few spirochetes present that they don’t cause a noticeable redness.

But they almost always have a rash that appears somewhere on the body. In patients who lack a visible lesion, physicians sometimes diagnose Lyme disease by testing their blood for antibodies to Borrelia burgdorferi.

tick on a person's finger

What Causes the Bull’s-Eye Rash?

The reason for the bull’s-eye pattern in some cases is not understood. But there are at least three theories:

  • The spirochete imitates erythrocytes or red blood cells, causing them to cluster around them in rings.
  • The bacteria cause inflammation, which recruits erythrocytes from nearby capillaries.
  • The spirochetes damage the endothelial cells or inner-lining cells of the blood vessels, which leads to leakage and recruitment of erythrocytes.

Fortunately, one cannot catch Lyme disease by being near a person who has the characteristic bulls-eye rash, and someone who has it cannot give the condition to somebody else. The disease is transmitted through deer ticks that bite their victims and then drop off. They don’t remain on their host long enough to transmit Borrelia burgdorferi.

Testing for Lyme Disease

The erythema migrans is just one of several possible skin conditions that can indicate Lyme disease. Lyme disease also causes facial paralysis, swelling near the eye, and inflammation of tendons and/or muscles.

It might be hard to believe that these non-specific signs could be related to Borrelia burgdorferi infection. However, one must remember that they are dealing with an organism capable of evading the immune system and persisting in the body for months and even years.

If such a rash occurs after a potential exposure to Lyme disease but is not accompanied by other signs and symptoms commonly associated with the condition (such as fever, headache, fatigue), it should be thoroughly evaluated even if it does not look like the classic bull’s eye.

The most common skin condition that resembles erythema migrans, in the absence of a deer tick bite, is called annular erythema with satellite lesions. This can occur in many infectious diseases, including HIV/AIDS, syphilis, rubella, and others.

Since it is difficult to make a diagnosis without knowing all the signs and symptoms of Lyme disease (including whether there was an associated rash), a physician might want to take a very detailed history from their patient(s) along with performing appropriate laboratory tests to determine if Lyme disease is present.

In some cases, a biopsy might be necessary, especially if additional testing continues to be negative despite clinical suspicion for Lyme disease.

If the history and clinical examination results suggest Lyme disease, appropriate laboratory tests should be performed to confirm the diagnosis. These might include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), or differential white cell count.

A positive serology test result is generally considered the single most reliable clue that the patient has been infected with Borrelia burgdorferi. Antibodies to the bacterium can be detected in serum via a sensitive enzyme-linked immunosorbent assay (ELISA) method.

In Lyme disease, the skin lesion might be accompanied by mild flu-like symptoms (fever and chills) and swollen glands. If untreated, patients will usually develop additional rashes at additional sites and arthritis, neurological problems, and heart rhythm irregularities.

Occasionally, patients complain of fatigue or body aches before developing a rash. Some, though, complain of long-term symptoms. Prompt treatment is necessary to avoid further complications, but tick prevention should remain a priority.

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