Borrelia burgdorferi is the tick-borne spirochete responsible for Lyme disease, and erythema migrans is the 1st cutaneous sign. Erythema migrans typically presents 1 to 2 weeks after the bite. The initial prodromal symptoms of fever, myalgias, arthralgias, and headache are followed by a macule or papule progressing to a plaque at the bite site. This plaque expands (usually to 5 cm or larger) its red, raised border as it clears centrally, leading to an annular appearance (“bull’s eye”). The plaque may burn and is rarely pruritic. Less frequently, secondary erythema migrans–like lesions can appear due to multiple bites or spirochetemia. Erythema migrans is seen in 60% to 90% of patients and represents the early localized stage.
Management and Disposition
The duration and choice of antibiotic depend on the features (presence of erythema migrans, early disseminated disease with mild or severe symptoms, cranial nerve palsies, heart block, meningitis, and radiculopathy). Doxycycline is the drug of choice for adults and children over 8 years of age. Pregnant or lactating females and children younger than 8 years of age should be treated with amoxicillin. Patients with minimal symptoms may be treated and followed up on an outpatient basis. Those patients with significant toxicity (severe disseminated rash, systemic symptoms, meningitis, radiculopathy, or third-degree heart block) require admission, supportive care, and IV antibiotics. Consult the Centers for Disease Control and Prevention (CDC) for the most up-to-date treatment regimen.
Over 50% of untreated cases of erythema migrans can progress to an asymmetric, episodic, oligoarticular arthritis weeks to months after the initial infection.
Facial nerve palsies are the most common neurologic manifestation of untreated Lyme disease.
Early serology testing may not demonstrate elevated anti-Borrelia antibodies, and this does not rule out the diagnosis. Follow current CDC case definitions and recommendations.
A similar erythema migrans–like rash has been described with the southern tick-associated rash illness (STARI).
Avoid Lyme disease single-dose doxycycline prophylaxis in areas endemic for Rocky Mountain spotted fever (RMSF); this inadequate treatment for RMSF could delay eventual RMSF diagnosis and treatment.
Erythema Migrans. The eruption of Lyme disease forms at the site of the tick bite. The initial papule forms into an expanding oval of erythema. There is central “bull’s eye” clearing as the erythema progresses. (Photo contributor: James Gathany, Public Health Image Library, US Centers for Disease Control and Prevention.)
Erythema Migrans. An atypical erythematous patch of erythema migrans—always have a high level of suspicion. (Photo contributor: David Effron, MD.)