What does a Lyme disease rash look like?

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Welcome to another Inside Lyme Podcast. I am your host Dr. Daniel Cameron. In this episode, I will be discussing a question I’m asked frequently: What does a Lyme disease rash look like? As a new study has found, the erythma migrans rash can appear differently based on several factors.

The study by Rebman and colleagues, entitled “The presenting characteristics of erythema migrans vary by age, sex, duration, and body location,” was published in Infection in March 2021.¹ It addressed a frequently asked question: What does a Lyme disease rash look like?

The erythema migrans (EM) rash (or Bull’s-eye rash), considered a definitive sign of Lyme disease, is often mistakenly thought to appear similar in all individuals – a circular red lesion which expands to at least 2 inches.

But as Rebman and colleagues report, a Lyme disease rash can look different based on several factors and does not always appear as the familiar Bull’s-eye rash. In fact, the authors suggest that relying solely on a Bull’s-eye appearance, when evaluating a rash for possible Lyme disease can lead to delays in diagnosis and treatment.

Diverse characteristics of Lyme disease rash

The authors examined 271 Lyme disease patients who had an erythema migrans rash to determine what does a Lyme disease rash look like? ¹

“We studied associations between these presenting characteristics [of EM rashes], as well as whether they were associated with age, sex, EM duration, body location, and initiation of antibiotics,” the authors write.

The patients were part of a longitudinal cohort study from 3 sites in Maryland and southeastern Pennsylvania. They were not enrolled if their rash was under 5 cm in diameter (2 inches) or their acute illness was longer than 3 months.

The study found that:

• EM size increased over time with the EM duration peaking at 14 days.
• Males had larger rashes than females (an average of 2.8 cm larger).
• Males were more likely to have a blue/red rash. In fact, the odds of a red rash in males was 65% lower than in females.
• Age was a significant predictor of central clearing. For every 10-year increase in age, the odds of central clearing decreased 25%. As age increased, there was a greater likelihood of a solid rash.
• EM rashes were more likely to occur in harder to see body locations (i.e.,  behind the thigh and behind the knees). The authors assumed that ticks had an opportunity to attach longer in these areas before being discovered.
• Nearly 1 in 3 patients had multiple rashes on examination.
• Approximately 1 in 3 patients reported pain at the site of the rash.  
• Just over 50% of the EM rashes were itchy.
• Rash shapes were varied ─ 50.9% were round; 39.1% were oval. The remaining rashes were irregular.
• Rash colors were varied ─ about 3 out of 4 were red. The remaining rashes were blue/red.
• Rash patterns were varied ─  only 28% appeared as a Bull’s-eye rash (a ring within the rash). Central lightness (17.3%), central darkness (28.8%) and uniform rashes (25.8%) were also described.
• Over 90% of the rashes were homogeneous. The remaining rashes were uneven.
• Nearly 9% presented with vesicles. 

Concerns with limiting size of Lyme disease rash

The authors raised concerns with following a 5 cm (or less than 2 inches) cutoff for EM rashes in determining the presence of a Lyme disease infection.

“Applying a 5 cm size cutoff in research or surveillance settings may thus exclude a higher proportion of females with otherwise suggestive clinical histories and epidemiological risk,” the authors write.

They also raised concerns about recognizing an EM rash in darker skinned patients. “95.9% of our final sample self-identified as non-Hispanic white.”

The authors suggest that the variation in EM rash presentations in males vs. females and among various ages may be related to an immune response to the Borrelia infection.

Authors’ Conclusion

“Given that EM remains a clinical diagnosis, it is essential that both physicians and the general public are aware of its varied manifestations.”

Editor’s note

Unfortunately, fewer than half of Lyme disease patients present with an erythema migrans rash. This case series merely reflects the diversity of rashes in Lyme disease patients fortunate enough to present with a rash.

The following questions are addressed in this episode:

• What is an erythema migrans rash?
• How often do Lyme disease patients have an erythema migrans rash?
• Can you culture Lyme disease from a rash?
• How long do erythema migrans rashes last?
• What other rashes resemble an erythema migrans rash?
• What color rashes have you seen?
• Where are rashes located?
• What is the significance of multiple rashes on examination?
• Have you seen itchy erythema migrans rashes?
• Can you discuss diversity of erythema migrans rashes that were described?
• Could a rash less than 2 inches in diameter be important?
• What do we know about the appearance of rashes in people of color?
• What is the importance of a smaller rash in women?

Thanks for listening to another Inside Lyme Podcast. You can read more about these cases in my show notes and on my website @DanielCameronMD.com. As always, it is your likes, comments, reviews, and shares that help spread the word about Lyme disease. Until next time on Inside Lyme.

Please remember that the advice given is general and not intended as specific advice to any particular patient. If you require specific advice, then please seek that advice from an experienced professional.