Snapshot A 16-year-old boy presents to his primary care physician with fatigue, malaise, and a rash. His symptoms began approximately 1 week ago and have progressively worsened. He said he recently hiked in northern Connecticut but is unsure if he was bitten by a tick. On physical exam, there is an erythematous and slightly raised lesion that appears "target-like" on the right thigh. He is given oral doxycycline. Introduction Definition login to view 10 more bullets Epidemiology Incidence login to view 1 more bullet Etiology Borrelia burgdorferi, a spirochete transmitted by the Ixodes tick login to view 3 more bullets Presentation Symptoms login to view 18 more bullets Differential Diagnosis Ehrlichiosis login to view 2 more bullets Studies Making the diagnosis login to view 1 more bullet Cerebrospinal fluid analysis when there is central nervous system involvement Synovial fluid analysis when arthritis is suspected Serologic studies login to view 1 more bullet Treatment Medical login to view 10 more bullets Prognosis The rash typically self-resolves without treatment Untreated Lyme disease can result in arthritis Excellent prognosis with early antibiotic treatment