Erythema Migrans: Diagnostic Clue or Criteria for Lyme disease?

Banik D and Chowdhury U

Published on: 2020-04-07


Erythema Migrans (EM) is a unique skin manifestation of Lyme disease. Early Lyme disease is a clinical diagnosis based on Erythema Migrans and possible exposure to the tick. There is no need to order Two-tired serologic testing to diagnose the condition. Though EM may present in different patterns other than classic Bull’s-eye (target lesion) appearance; only the Bull’s-eye pattern of EM is pathognomonic for Lyme disease.


Erythema migrans; Lyme disease

Case Description

A 54-year-old Nepali immigrant male in New York City with medical history of coronary artery disease, hypertension, and hyperlipidemia presented to a primary care physician office with high grade fever and skin rash on his right loin. He reported the rash started 5 days back, without any known contact to offending agent, initially small, gradually progressive, red in color, painless, non-itchy, and non-discharging. It is associated with high grade continued fever, malaise, and generalized fatigue. Patient reported of going to New Jersey for a trail walk 7 days back. On query, he denied chest pain, shortness of breath, palpitation, joint pain, joint swelling, headache, neck pain, facial deviation, and tingling/numbness/weakness in limbs, skin rashes in other parts of the body, and tick identification or removal. On physical examination, temperature was recorded 102 F, tachycardic, and a moderately tender enlarged lymphnode in the right posterior axillary chain. A homogenous, erythematous, non-tender, non-discharging patch was noted on the right lumbar region (Figure 1A). The rash was oval, 3.5”x2” in size, blanches on pressure, with regular margin and a punctum on the center (Figure 1B).

Figure 1: Erythema Migrans- an oval, erythematous, homogenous patch with a central punctum and regular margin. (A and B).

Clinical diagnosis was made Eryhtema Migrans of Early Localized Lyme Disease. Patient was treated with oral Doxycycline 100 mg twice daily for 14 days. On subsequent follow up after 2 weeks, patient presented with complete resolution of sign and symptoms.

Discussion and Conclusion

Erythema Migrans (EM) is a unique cutaneous manifestation of Early Lyme Disease that develops at the site of inoculation of the causative spirochete Borrelia burgdorferi by the vector Ixodes species [1]. Around 70-80% of patients with Lyme Disease have presented with EM in 7- 14 days (range, 3-30 days) after the exposure to the tick [2,3]. Primary solitary EM should be at least 5 cm in largest diameter to secure the diagnosis [3]. Other than the classic Bull’s-eye (target lesion) appearance, EM may present as expanding rash with central crust, disseminated infection, oval plaque, triangular lesion, central vesicular lesion, expanding rash with central clearing, and bluish rash with/without central clearing [1,4]. Despite of being the classic presentation- only the Bull’s-eye pattern is the pathognomonic for Lyme disease [5]. It is always challenging for the clinicians to differentiate EM from other ‘look-alikes’ dermatologic conditions like insect bite hypersensitivity, southern tick-associated rash illness, cellulitis, Herpes simplex, Varicella zoster, contact dermatitis, drug reaction, tinea corporis, pityriasis rosea, granuloma annulare, and urticaria multiforme [1,4]. Early Lyme Disease can be diagnosed on clinical grounds alone based on endemicity and objective skin lesion consistent with EM. Two-tired serologic testing is not recommended in early Lyme disease (sensitivity 30-40%) as antibodies to B. burgdorferi may take two to four weeks to be appeared- resulting in false negative result [2,6]. So, this is very important to diagnose EM clinically considering patient’s risk of exposure to the tick, and to treat with the appropriate antibiotic immediately to avoid the possible multi-system complications that may arise from dissemination of the bacteria.