Lyme disease. Recognising and treating erythema migrans.

Lyme disease is a tick-borne bacterial infection caused by Borrelia spirochetes. The first stage of infection involves a characteristic skin lesion, erythema migrans. Erythema migrans is a ring-shaped skin lesion, centred on the bite, which expands outwards. It usually appears within two weeks after a bite from an infected tick. If left untreated, the infection sometimes extends or progresses over a period of months or years, leading to potentially severe neurological, articular, cutaneous and cardiac complications. How is erythema migrans associated with Lyme disease recognised and managed? We conducted a systematic review of the literature using the standard Prescrire methodology. This review does not address the complications of Lyme disease. Diagnosis of erythema migrans is based on clinical findings in a patient with a possible or confirmed recent tick bite. Serological tests are not useful at this stage of the infection. Antibiotics shown to be active in vitro also proved effective in non-comparative trials. In randomised trials, amoxicillin, doxycycline, cefuroxime and ceftriaxone had similar efficacy, clearing signs and symptoms in about 90% of patients, with a relapse rate of less than 5% at 6 months. Azithromycin, clarithromycin, erythromycin, three macrolide antibiotics, appear to have lower efficacy. Doxycycline should not be used to treat pregnant or breast-feeding women, or children under 8 years old, due to a risk of tooth and bone disorders in children. In practice, a diagnosis of erythema migrans should be borne in mind when a patient presents with recent history of a possible or confirmed tick bite and skin lesions suggestive of erythema migrans. Oral amoxicillin or doxycycline will prevent progression of the infection to the potentially severe, later stages of Lyme disease. Routine antibiotic prophylaxis is not justified after a tick bite, even in an endemic area, as the risk of infection is low. It is best to monitor the skin around the bite and to prescribe an antibiotic only if erythema migrans develops, thus avoiding unnecessary treatment and adverse effects.