How is Lyme disease acquired, what are its typical symptoms, and what red‑flag features indicate serious complications?

How Lyme Disease is Acquired

Lyme disease is transmitted through the bite of infected Ixodes species ticks (deer ticks) that carry the spirochete Borrelia burgdorferi, with transmission occurring when the tick remains attached for typically 36-48 hours. 1

Transmission Details

• The disease is a tick-borne zoonosis caused by genospecies of the Borrelia burgdorferi sensu lato complex 1
• In North America, B. burgdorferi causes nearly all infections, while in Europe, B. afzelii and B. garinii are most commonly associated with human disease 1
• Ticks from the Ixodes ricinus complex serve as the vectors, with humans being incidental hosts 1
• The spirochete is deposited into human dermal tissue during the tick bite, generating a local inflammatory response 1

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Clinical Symptoms by Stage

Early Localized Disease (Days to Weeks After Bite)

The hallmark early manifestation is erythema migrans (EM), an expanding erythematous skin lesion that develops days to weeks following the tick bite. 2

• EM appears at a median of 7-14 days after tick exposure 2
• The classic "bullseye" rash with central clearing is common but not universal 3
• Diagnosis is based on the appearance of the skin lesion rather than laboratory testing 2
• If treated appropriately and early with oral antibiotics for 10-14 days, the prognosis is excellent 2

Early Disseminated Disease (Weeks to Months)

Untreated patients may develop neurologic (11%), cardiac (4-8%), or additional skin manifestations. 4

Neurologic Manifestations

• Cranial neuritis (most commonly unilateral or bilateral facial nerve palsy) 5
• Meningitis with CSF pleocytosis 5
• Radiculoneuritis/mononeuropathy multiplex with painful radiculitis involving spinal cord segments 6, 5

Cardiac Manifestations

• Cardiac complications occur at a median of 21 days from onset of EM 7
• Atrioventricular block (most common cardiac finding) 7
• Myopericarditis with elevated troponin 6
• Symptoms include dyspnea, palpitations, lightheadedness, chest pain, syncope, and edema 6
• Up to one-third may require temporary cardiac pacing 7

Ocular Manifestations

• Uveitis (45% of ocular cases) 8
• Optic neuritis and cranial nerve palsies (trochlear and abducens nerves) 8

Late Disseminated Disease (Months to Years)

Approximately 45-60% of untreated patients develop Lyme arthritis, typically affecting large joints. 4

• Arthritis was the original defining feature when the disease was first identified in Lyme, Connecticut 4
• Serum antibody testing is recommended over PCR or culture for diagnosis 6

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Red Flag Features Requiring Urgent Intervention

Cardiac Red Flags

Patients with PR interval >300 milliseconds, other arrhythmias, or clinical manifestations of myopericarditis require hospital admission with continuous ECG monitoring. 6

• Symptomatic bradycardia that cannot be managed medically requires temporary pacing rather than permanent pacemaker implantation 6
• Perform ECG in patients with signs or symptoms consistent with Lyme carditis: exercise intolerance, palpitations, presyncope, syncope, pericarditic pain, pericardial effusion, elevated biomarkers, edema, or shortness of breath 6

Neurologic Red Flags

Test for Lyme disease in patients presenting with acute meningitis, cranial neuritis (especially facial palsy), or radiculoneuritis with epidemiologically plausible tick exposure. 6

• Parenchymal involvement of the brain or spinal cord requires IV antibiotics over oral therapy 6
• Central nervous system infection is confirmed by CSF pleocytosis or pathogen-specific intrathecal antibody production 5

Cardiac Emergency Indicators

Acute myocarditis/pericarditis of unknown cause in an appropriate epidemiologic setting warrants immediate testing for Lyme disease. 6

• Hospitalized patients with Lyme carditis should initially receive IV ceftriaxone until clinical improvement, then switch to oral antibiotics 6

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Common Pitfalls to Avoid

• Do not routinely test patients with psychiatric illness, typical ALS, relapsing-remitting MS, Parkinson's disease, dementia, or new-onset seizures for Lyme disease 6
• Do not test for chronic cardiomyopathy of unknown cause as routine practice 6
• Do not provide prolonged or recurrent antibiotic treatment for post-treatment Lyme disease syndrome (PTLDS), as there is no evidence this changes natural history 4, 9
• Serologic features are often misinterpreted; confirmatory Western blot testing must follow positive or borderline ELISA results 5
• Approximately 10% of patients may develop PTLDS (fatigue, diffuse pain, cognitive dysfunction lasting >6 months) despite appropriate treatment, which requires multidisciplinary supportive care rather than additional antibiotics 1, 9