An erythema migrans otherwise known as an EM, is the rash associated with Lyme disease. The rash does not occur in every case of Lyme disease but if a patient does present with an EM rash then no blood test is required and treatment should be prescribed immediately as per the NICE guidelines.
Throughout the year we see a variety of EM rashes shared on social media and the key thing to take away from it is that the EM rash comes in many forms. Rarely do you see a ‘neat and tidy’ bullseye rash like the picture below.
It is thought that there are five main types of EM and that the bullseye rash is not actually the most common. This is important to remember in order to avoid a misdiagnosis. If you develop any kind of rash, you should seek prompt medical advice.
In order to correctly diagnose an EM rash, the following characteristics are key considerations:
- An EM rash typically appears after the third day of infection and according to information on the NHS website, can take up to three months to appear (if at all).
- An EM rash will most often appear at the site of the bite and will grow outwards as it progresses. We always advise to draw around the rash with a biro each day to monitor the changing size.
- An EM rash isn’t usually hot, itchy or raised but some patients have reported experiencing these things.
- An EM rash won’t normally respond to antihistamines or antifungal cream.
- It’s not unheard of to present with multiple EM rashes across the body, even if you were only bitten once.
- An EM rash won’t always have a central clearing, and may have a central blister.
- An EM rash is often circular or oval, but may also appear blotchy.
- An EM rash can be red, blue and/or purple, and sometimes a yellowing colour can appear, though this may not be the case for people with darker skin tones. Read this blog from Dr Z Husain Skin Colour, Medical Education and Erythema Migrans – Room for Improvement for more information about skin colour and the EM rash.
The following images and information are available to download from the NICE Lyme disease tools and resources section and detail ten different types of the EM rash. Click on the images to enlarge them.
Always seek medical advice, ideally from a GP who has passed the RCGP Lyme disease course. If your doctor isn’t sure whether you have an EM rash or cellulitis, they may be able to prescribe an antibiotic that could treat both infections.
For further images and information on Lyme disease and the associated rashes, please see the below resources:
- ‘What does a Lyme disease rash look like?’ From Medical News Today
- ‘Signs of Lyme disease that appear on your skin’ from The American Academy of Dermatology
- ‘Lyme Disease Rashes and Look-alikes’ from the CDC
- ‘Does everyone get the telltale bullseye rash?’ from The Bay Area Lyme Foundation
- ‘Bull’s-Eye and Nontarget Skin Lesions of Lyme Disease: An Internet Survey of Identification of Erythema Migrans’ available on The NCBI website
- ‘Looking for a bull’s-eye rash? Look again – erythema migrans can take many forms.’ An educational poster from Maryland Department of Health and Mental Hygiene and the Lyme Disease Research Foundation of Maryland.