The presenting characteristics of erythema migrans vary by age, sex, duration, and body location

Purpose: The erythema migrans (EM) skin lesion is often the first clinical sign of Lyme disease. Significant variability in EM presenting characteristics such as shape, color, pattern, and homogeneity, has been reported. We studied associations between these presenting characteristics, as well as whether they were associated with age, sex, EM duration, body location, and initiation of antibiotics. Methods: Two hundred and seventy one adult participants with early Lyme disease who had a physician-diagnosed EM skin lesion of ≥ 5 cm in diameter and ≤ 72 h of antibiotic treatment were enrolled. Participant demographics, clinical characteristics, and characteristics of their primary EM lesion were recorded. Results: After adjusting for potential confounders, EM size increased along with increasing EM duration to a peak of 14 days. Male EM were found to be on average 2.18 cm larger than female EM. The odds of a red (vs blue/red) EM were 65% lower in males compared to females, and were over 3 times as high for EM found on the pelvis, torso, or arm compared to the leg. Age remained a significant predictor of central clearing in adjusted models; for every 10-year increase in age, the odds of central clearing decreased 25%. Conclusions: Given that EM remains a clinical diagnosis, it is essential that both physicians and the general public are aware of its varied manifestations. Our findings suggest possible patterns within this variability, with implications for prompt diagnosis and treatment initiation, as well as an understanding of the clinical spectrum of EM.