The child's presentation is consistent with Lyme disease, caused by Borrelia burgdorferi and transmitted by the Ixodes tick. First line treatment for children < 8 years old with early localized Lyme disease is amoxicillin.
Lyme disease, commonly seen in North American summers, can present in several stages: early localized, early disseminated, and late disseminated. Early localized classically presents with a "bullseye" rash known as erythema migrans (EM), plus or minus systemic symptoms (malaise, fever, chills, myalgias, headache). Early disseminated disease can present with Bell's palsy, carditis (pericarditis or AV block), or multiple EM. Late disseminated disease presents with large joint arthritis, peripheral neuropathy, encephalopathy, or acrodermatitis chronica atrophicans.
Wright et al. review the diagnosis and treatment of Lyme disease. EM is the only physical findings sensitive enough for diagnosis. The CDC recommends serologic testing with an ELISA (and Western blot for confirmation). Prevention is important as is prompt treatment.
Klempner et al. review four randomized controlled trials that have evaluated whether benefit exists for prolonged antibiotic treatment for those with "chronic Lyme," a controversial term used by patients with a variety persistent symptoms post-treatment. Initial analysis of these 4 studies showed no benefit and significant risk from continued treatment. An independent analysis claimed benefit did exist. These authors refute that finding.
Figure A depicts EM, which occurs in most patients (80% of adults, 60% of children). Presence of the rash has 81% sensitivity for the disease.
Illustration A shows a Ixodes tick, also known as a deer tick, the main vector of Lyme disease in North America.
Illustration B depicts the life cycle of a Ixodes tick. This chart emphasizes that most transmissions occur in summer months, as this is when the nymph ticks, who transmit the disease, are feeding.
Answer 2: Doxycycline is first-line treatment for patients older than 8 years old. Tetracycline antibiotics are avoided in young children because they can cause permanent staining of the teeth.
Answer 3: Azithromycin, or other macrolide antibiotics, are reserved as second line treatment for patients who cannot tolerate amoxicillin, doxycycline, or cefuroxime.
Answer 4: First-generation cephalosporins are ineffective against Lyme.
Answer 5: The IDSA recommends against ceftriaxone as first-line treatment for early localized Lyme, as it is associated with more severe side effects. It is recommended for early disseminated Lyme as well as some late Lyme manifestations.
Wright WF, Riedel DJ, Talwani R, Gilliam BL. Diagnosis and management of Lyme disease. Am Fam Physician. 2012 Jun 1;85(11):1086-93.
PMID:22962880 (Link to Abstract)
Klempner MS, Baker PJ, Shapiro ED, Marques A, Dattwyler RJ, Halperin JJ, Wormser GP. Treatment trials for post-Lyme disease symptoms revisited. Am J Med. 2013 Aug;126(8):665-9. doi: 10.1016/j.amjmed.2013.02.014. Epub 2013 Jun 10.
PMID:23764268 (Link to Abstract)