Lyme disease presents with an eruption that begins as an erythematous papule at the bite's site and progresses to an annular erythema that may be greater than 20 cm. It may form a ring or multiple rings in a "bull's eye" conformation. This 5 to 20 cm eruption is called erythema chronicum migrans. Half of patients afflicted with Lyme disease will develop multiple secondary annular rings which begin 1 to 6 days after the primary lesion appears. In addition to the rash, the patient may develop fever, malaise, headache and arthralgias. Joint, CNS, and cardiac abnormalities are later manifestations and begin after spontaneous resolution of the erythema chronicum migrans. Bell's palsy is very common with Lyme disease.

Differential diagnosis

The differential for erythema chronicum migrans includes many annular erythemas such as erythema annulare, erythema annulare centrifugum, erythema marginatum, tinea corporis, pityriasis rosea, sarcoidosis, syphilis, juvenile rheumatoid arthritis, cutaneous lupus erythematosus and insect bite reaction.

Pathophysiology

Lyme disease is caused by a spirochete, Borrelia burgdorferi, which is transmitted by the Ixodes tick.

Treatment

Young children are treated with amoxicillin and children over 8 years of age may be treated with tetracycline or doxycycline. If meningitis or heart block is present, then IV ceftriaxone or penicillin is recommended. The importance of completing the antibiotic therapy should be emphasized to the parent to avoid complications of the disease.