Diagnosis, treatment, and prognosis of erythema migrans and Lyme arthritis.

Most patients with erythema migrans, the pathognomonic rash of Lyme disease, do not recall a deer tick bite. The rash is classically 5 to 68 cm of annular homogenous erythema (59%), central erythema (30%), central clearing (9%), or central purpura (2%). Serologic testing is not indicated for patients with erythema migrans, because initially, the result is usually negative. Successful treatment of a patient with erythema migrans can be accomplished with 20 days of oral doxycycline, amoxicillin, or cefuroxime axetil. Patients with Lyme arthritis usually present with a mildly painful swollen knee. Patients with Lyme arthritis have markedly positive serology and can usually be successfully treated with 28 days of oral doxycycline or amoxicillin. Some patients may have persistent effusion despite 4 to 8 weeks of antibiotics and may need synovectomy. Persistent effusion is not due to persistent infection. Antibiotic therapy for more than 8 weeks for patients with Lyme disease is not indicated. Chronic Lyme disease due to antibiotic resistant infection has not been demonstrated.