Overview
Definition
A tick-borne illness caused by the spirochete Borrelia burgdorferi.
Epidemiology
The most common vector-borne disease in the US, primarily in the Northeast and upper Midwest.
Etiology & Risk Factors
- Borrelia burgdorferi transmitted by the bite of an infected Ixodes scapularis (deer) tick. The tick must be attached for at least 36-48 hours to transmit the bacteria.
Clinical Symptoms
- Early Localized (Days-Weeks): Erythema migrans (classic 'bulls-eye' rash), fatigue, myalgias, arthralgias, fever
- Early Disseminated (Weeks-Months): Multiple smaller EM rashes, Bell's palsy (cranial nerve VII palsy, often bilateral), AV block (Lyme carditis)
- Late Disseminated (Months-Years): Lyme arthritis (migratory, asymmetrical, large joints like the knee), Encephalopathy
Clinical Approach
Diagnosis
- Clinical diagnosis if Erythema Migrans is present (especially in an endemic area)
- Two-Tiered Serologic Testing (for disseminated disease): Enzyme immunoassay (EIA) or immunofluorescence assay (IFA), followed by a Western blot if positive/equivocal
Management
- Early Localized / Early Disseminated: Oral Doxycycline for 10-21 days (Amoxicillin or Cefuroxime for children <8 years and pregnant women)
- Lyme Carditis or Neurologic (Meningitis/Encephalitis): IV Ceftriaxone
- Prophylaxis: Single dose of Doxycycline if tick is attached > 36 hours in an endemic area
Complications
- Chronic Lyme arthritis
- Permanent neurological deficits (rare)