Lyme disease is caused by the bacterium Borrelia burgdorferi, spread by blacklegged ticks mostly in the Northeast and upper Midwest of the US. It often starts with a spreading rash and, if untreated, can affect the joints, nerves and heart.
Key symptoms
- Expanding red rash at the bite site days to weeks later
- Fever, chills, fatigue, headache and muscle aches
- Facial weakness on one or both sides
- Palpitations, dizziness or fainting
- Swollen, painful knee weeks to months later
What you find on exam
- Erythema migrans: red patch 5 cm or larger, sometimes with central clearing
- Several rash patches when the infection has spread
- Cranial nerve exam for facial palsy; signs of meningitis
- Slow or irregular pulse
- Large knee effusion with little warmth
Tests
- Erythema migrans is a clinical diagnosis; no testing needed
- Two-tier serology (screening test, then confirmatory test) for later stages
- ECG if heart symptoms: look for AV block
- Joint fluid analysis or lumbar puncture in selected cases
Treatment basics
- Doxycycline for early disease; amoxicillin or cefuroxime as alternatives
- Oral doxycycline also works for facial palsy and most nerve disease
- IV ceftriaxone for high-degree heart block or meningitis
- Oral antibiotics for about 4 weeks for Lyme arthritis
- Single dose of doxycycline after a high-risk tick bite in selected patients
Red flags
- Fainting, very slow pulse or high-degree heart block
- Severe headache with stiff neck
- Weakness or numbness spreading in the limbs
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.