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Key Features

Essentials of Diagnosis

  • Characteristic skin lesion (erythema migrans) 3–30 days after tick bite

  • Arthritis, usually pauciarticular, occurring about 4 weeks after appearance of skin lesion

  • Headache, chills, and fever

  • Residence or travel in an endemic area during the late spring to early fall

General Considerations

  • Caused by Borrelia burgdorferi

  • Transmitted by an infected deer tick (Ixodes species)

  • Most cases with rash are recognized in spring and summer, when most tick bites occur

  • However, because the incubation period for joint and neurologic disease may be months, cases may present at any time


  • The most prominent endemic areas in the United States include the Northeast, upper Midwest, and West Coast

  • Northern European countries also have high rates of infection

Clinical Findings

Symptoms and Signs

  • Erythema chronicum migrans

    • Most characteristic feature of Lyme disease

    • Recognized in 60–80% of patient

    • Ring of erythema develops at the site and spreads over days

    • May attain a diameter of 20 cm

    • Center of the lesion may clear (resembling tinea corporis), remain red, or become raised

    • Mild tenderness may occur

    • Untreated, the rash lasts days to 3 weeks

  • Most patients are otherwise asymptomatic

  • Some have fever (usually low-grade), headache, and myalgias

  • Multiple satellite skin lesions, urticaria, or diffuse erythema may occur

  • Arthritis

    • Develops several weeks to months after the bite in up to 50% of patients

    • Recurrent attacks of migratory, monoarticular, or pauciarticular arthritis involving the knees and other large joints occur

    • Each attack lasts for days to a few weeks

    • Fever is common and may be high

    • Complete resolution between attacks is typical

    • Chronic arthritis develops in < 10% of patients, more often in those with the DR4 haplotype

  • Neurologic manifestations

    • Develop in up to 20% of untreated patients

    • Usually consist of Bell palsy, aseptic meningitis, or polyradiculitis

    • Peripheral neuritis, Guillain-Barré syndrome, encephalitis, ataxia, chorea, and other cranial neuropathies are less common

    • Usually self-limited if left untreated but may be chronic or permanent

Differential Diagnosis

  • Rash may resemble pityriasis, erythema multiforme, a drug eruption, or erythema nodosum

  • Arthritis may resemble juvenile rheumatoid arthritis, reactive arthritis, septic arthritis, reactive effusion from a contiguous osteomyelitis, rheumatic fever, leukemic arthritis, systemic lupus erythematosus, and Henoch-Schönlein purpura


  • Clinical; serologic testing may support the clinical diagnosis

  • Serologic diagnosis of Lyme disease is based on a two-test approach: an ELISA and an immunoblot to confirm a positive or indeterminate ELISA

  • Antibodies may not be detectable until several weeks after infection has occurred; therefore, serologic testing in children with a typical rash is not recommended

  • Children with arthritis

    • May have moderately elevated ESRs and WBC counts

    • Antinuclear antibodies and rheumatoid factor tests are negative or nonspecific

    • Streptococcal antibodies are not elevated


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