Not All Erythema Migrans Lesions Are Lyme Disease

Lyme disease is the number one arthropod-transmitted disease in the US, and one of the diagnostic criteria for the illness is development of an erythematous bull's-eye rash around a tick bite that may expand over time, hence the term erythema migrans. However, there are other erythema migrans-like rashes, such as those from a condition known as southern tick-associated rash illness. This article describes a patient with an erythema migrans-like lesion similar to that associated with Lyme disease, resulting from a bite by a nymphal-stage lone star tick, Amblyomma americanum.

A tick removed from the center of an erythema migrans-like lesion in a patient was identified to species and then submitted to the Centers for Disease Control and Prevention for testing for the agent of Lyme disease, Borrelia burgdorferi. The patient was evaluated by an internist 7 weeks later. After another 3 weeks, the patient's blood was tested serologically for Lyme disease by American Esoteric Laboratories, Memphis, Tenn.

Both the tick and human blood sample from this patient were negative for evidence of Lyme disease. Clinically, other than the erythema migrans-like lesion, the patient displayed no signs or symptoms consistent with Lyme disease.

This case presents clinical, serological, and molecular evidence that erythema migrans lesions may occur after tick bites in patients and that these lesions may not be due to infection with the agent of Lyme disease.