Conditions · Infectious and tropical diseases
Lyme disease !
Lyme disease is a tick-borne bacterial infection with a spreading bull's-eye rash; untreated, it can affect the nerves, heart and joints.
Updated 2026-11-01
Structures involved
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Microorganisms that cause it
Why it happens
What it is
An infection by Borrelia burgdorferi sensu lato, transmitted by Ixodes ticks, that starts as a skin rash and can spread to the nervous system, heart and joints.
Who gets it
The most common vector-borne disease in the United States and frequent in Europe and parts of Asia. It is not considered endemic in Colombia or most of Latin America; cases there are usually imported. It is high-yield on the USMLE and NCLEX.
Causes
- Borrelia burgdorferi in North America; B. afzelii and B. garinii in Europe and Asia
- Spread by the bite of Ixodes (blacklegged or deer) ticks, usually nymphs
- Transmission usually needs more than 36 hours of tick attachment
Risk factors
- Living in or travelling to endemic areas (northeastern and upper midwestern United States, Europe)
- Outdoor activities in woods and grassland in late spring and summer
- Not using repellents or not checking for ticks
- Pets that bring ticks into the home
Pathophysiology
Spirochaetes multiply in the skin at the bite site and spread outward, producing erythema migrans. They then disseminate through blood and lymph to other skin sites, nerves, meninges, heart and joints. Much of the tissue damage is due to the host inflammatory response; persistent arthritis in some patients is immune mediated after the bacteria are cleared.
Classification
- Early localised: erythema migrans with or without flu-like symptoms (days to a month)
- Early disseminated: multiple erythema migrans, cranial neuropathy, meningitis, radiculopathy, carditis (weeks to months)
- Late: arthritis, usually of the knee; rarely late neurological disease (months to years)
Symptoms and signs
- Erythema migrans: an expanding red rash at least 5 cm across, sometimes with central clearing (bull's eye)
- Fever, chills, headache, fatigue, muscle and joint aches
- Facial palsy, often bilateral
- Shooting radicular pain, numbness or meningitis-type headache and stiff neck
- Palpitations, light-headedness or fainting from heart block
- Episodes of swelling of one or a few large joints, especially the knee
Diagnosis
- Clinical
- Erythema migrans after possible tick exposure in an endemic area is enough to diagnose early Lyme disease and treat, without testing.
- Tests
- Serology in two steps (immunoassay followed by a confirmatory test) for disseminated or late disease; antibodies may be negative in the first weeks. ECG in anyone with cardiac symptoms or early disseminated disease. Lumbar puncture when meningitis is suspected; joint aspiration for arthritis (synovial PCR can help).
- Imaging
- Not needed for most patients; echocardiography in carditis, MRI of the brain in atypical neurological disease.
Differential diagnosis
- Cellulitis or local tick-bite reaction
- Idiopathic Bell palsy
- Viral meningitis
- Septic arthritis and reactive arthritis
- Juvenile idiopathic arthritis
- Other tick-borne infections (rickettsial disease, anaplasmosis, babesiosis)
Goal of treatment
Cure the infection early to prevent spread to nerves, heart and joints, and manage cardiac conduction disturbances safely.
Treatment
- Medical
- Oral antibiotics for early disease and most arthritis or isolated facial palsy: doxycycline, or amoxicillin or cefuroxime as alternatives.
- Medical
- Intravenous ceftriaxone for meningitis, severe carditis or arthritis that does not respond to oral treatment.
- Acute
- Hospital admission with ECG monitoring for high-grade heart block; a temporary pacemaker may be needed; the block usually resolves.
- Follow-up
- Follow-up of symptoms after treatment; some patients have fatigue, pain or difficulty thinking for months (post-treatment Lyme disease syndrome), which does not respond to longer antibiotics.
Complications
- Lyme carditis with atrioventricular block
- Facial nerve palsy and other cranial neuropathies
- Lymphocytic meningitis and radiculoneuritis
- Lyme arthritis, sometimes persistent after antibiotics
- Post-treatment Lyme disease syndrome
Prognosis
Most patients treated early recover completely. Late disease also responds to antibiotics, though arthritis or post-treatment symptoms can persist for months.
Prevention
- Repellents, long sleeves and trousers in tick habitats
- Daily tick checks and removal of ticks with fine tweezers
- A single dose of doxycycline after a high-risk tick bite in endemic areas in selected cases
- Tick control for pets and yard management
Test yourself
Think of the answer, then tap the question to see it.
What tick transmits Lyme disease in North America?
Ixodes (blacklegged or deer) ticks, usually nymphs attached for more than 36 hours.
What is the classic skin lesion of early Lyme disease?
Erythema migrans: an expanding red rash at least 5 cm across, often with central clearing (bull's eye).
Which cardiac complication of Lyme disease may need a temporary pacemaker?
Atrioventricular (heart) block due to Lyme carditis.
What cranial nerve finding suggests early disseminated Lyme disease?
Facial nerve palsy, especially when bilateral.
Related conditions
- Bell palsy
- Atrioventricular (heart) block
- Myocarditis
- Septic Arthritis of the Knee
- Reactive arthritis
- Juvenile idiopathic arthritis
- Bacterial meningitis
- Cellulitis of the leg
- Rickettsial infections (spotted fever)
- Fibromyalgia
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Lyme disease: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2024); Clinical Care of Lyme Disease | Lyme Disease | CDC (Centers for Disease Control and Prevention, 2024).
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