Author:

• Anita Savell

Deputy Editor:

• Stormy Foster-Palmer

Publish date: Posted on March 8, 2021February 17, 2024
Last updated: February 17, 2024

Keywords #

erythema migrans
borellia burgdorferi
Lyme disease
Lyme borreliosis

Diagnosis #

Erythema migrans (EM) is a cutaneous manifestation of early Lyme disease. Lyme disease is a tick-borne illness caused by the spirochete Borreliella. EM is a rash that appears at the site of a tick bite. While EM is self-limiting, Lyme disease should be treated with an appropriate antibiotic regimen as it may spread to the central nervous system, heart, or joints and can be associated with significant morbidity.

Key Concepts #

• EM is a self-resolving sign of early Lyme disease.
• EM allows for a clinical diagnosis of Lyme disease and does not require confirmatory testing.
• Lyme disease must be treated with antibiotics to prevent systemic disease.

Epidemiology #

Lyme disease is most commonly seen in the northeastern region of the United States. While anyone may become infected, Lyme disease is most frequently seen in people aged 5-15 years and 45-55 years during the summer months who participate in outdoor activities such as hiking or gardening. [2] Many patients with EM do not remember a preceding tick bite. [1]

Clinical Features #

• EM is classically described as a targetoid lesion; however, lesions can be homogenous as well. It begins as an erythematous macule that expands over days to weeks and can reach a size of up to 20cm.[1]
• A punctum representing the location of a tick bite may be appreciated in the center of the lesion. [3]
• Color varies between lesions and may be pink, red, and blue. EM may be faint or difficult to recognize on patients with darker skin tones.[1]
• Patients may report other symptoms of early Lyme disease such as fever, chills, and myalgias.
• Multiple EM lesions may indicate early disseminated disease.[2]
• EM self resolves in a median of 4 weeks. [1]

Differential Diagnoses #

• Arthropod bites
• Contact dermatitis
• Tinea (tinea corporis, tinea capitis, tinea cruris, tinea pedis, barbae)
• Urticaria
• Urticaria (or similar appearing lesions) can also occur in urticarial vasculitis, autoimmune diseases, malignancies, and mastocytosis.
• Cellulitis
• Drug eruptions
• Simple drug eruptions
• Morbilliform drug eruption

Diagnostic Workup #

EM is a clinical diagnosis. If one or more characteristic EM lesion is present in a patient who lives in or has recently traveled to an endemic area, the diagnosis of EM should be made. These patients do not require confirmatory serological testing.

Treatment #

EM lesions will self-resolve without treatment. Early Lyme disease for which EM is diagnostic, however, requires treatment with antibiotics such as doxycycline, amoxicillin, or cefuroxime. Antibiotic selection and duration are dependent on patient age, likelihood of co-infection, and severity of disease. Treatment for Lyme disease reduces the duration of the EM lesion. [4]

Slide Viewer #

https://utahderm.med.utah.edu/image-viewer/

References #

1. Nadelman RB. Erythema migrans.Infect Dis Clin North Am. 2015;29(2):211-239. doi:10.1016/j.idc.2015.02.001
2. Steere AC, Strle F, Wormser GP, et al. Lyme borreliosis [published correction appears in Nat Rev Dis Primers. 2017 Aug 03;3:17062].Nat Rev Dis Primers. 2016;2:16090. Published 2016 Dec 15.
3. Shimamura Y, Maeda T, Gocho Y. Tick bite-Erythema migrans.J Gen Fam Med. 2018;19(2):59-60. Published 2018 Jan 18. doi:10.1002/jgf2.152
4. Branda JA , Strle K , Nigrovic LE et al. Evaluation of modified 2-tiered serodiagnostic testing algorithms for early Lyme disease. Clin Infect Dis 2017; 64:1074–80.