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 a tick-borne illness characterized by 3 stages early localized stage (within 1 month of the tick bite) erythema migrans early disseminated stage multiple erythema migrans neurological symptoms (e.g., facial nerve palsy, meningitis, and mononeuritis multiplex) cardiac symptoms (e.g., carditis) late stage arthritis encephalopathy or polyneuropathy Epidemiology Incidence most cases in the northeast and upper midwest Etiology Borrelia burgdorferi, a spirochete transmitted by the Ixodes tick this tick is also a vector for Anaplasma spp. Babesia microti Presentation Symptoms early localized stage erythema migrans (7-14 days post-tick bite) round erythema that expands and can result in the classic target lesion may be accompanied by systemic symptoms such as fevers myalgias arthralgias headache fatigue early disseminated stage multiple erythema migrans neurological symptoms (e.g., facial nerve palsy, meningitis, and mononeuritis multiplex) lyme carditis may present as an atrioventricular block and/or myopericarditis late stage arthritis the knees are classically involved encephalopathy or polyneuropathy Differential Diagnosis Ehrlichiosis fever, malaise, aches, without a rash leukopenia, thrombocytopenia and elevated aminotransferases Studies Making the diagnosis this is a clinical diagnosis Cerebrospinal fluid analysis when there is central nervous system involvement Synovial fluid analysis when arthritis is suspected Serologic studies performed to support the clinical diagnosis Treatment Medical doxycycline or amoxicillin indication erythema migrans Lyme arthritis macrolides can be used in patients who are allergic to doxycycline, ceftriaxone, and cefuroxime ceftriaxone indication neurologic Lyme disease Lyme carditis Prognosis The rash typically self-resolves without treatment Untreated Lyme disease can result in arthritis Excellent prognosis with early antibiotic treatment