SUPERStudy: Lyme Disease

By usmlevideoss

Introduction

Lyme disease is a multisystemic infectious disease caused by the spirochete Borrelia burgdorferi, transmitted through the bite of infected Ixodes ticks (black-legged or deer ticks). It is the most common tick-borne illness in the United States and Europe and can cause dermatologic, neurologic, cardiac, and musculoskeletal complications.

Etiology

  • Causative Agent: Borrelia burgdorferi (in North America), Borrelia afzelii and Borrelia garinii (in Europe and Asia).
  • Vector: Ixodes ticks (Ixodes scapularis in the U.S., Ixodes ricinus in Europe).
  • Reservoirs: White-footed mice, deer, and small mammals.
  • Transmission: Bite of an infected Ixodes tick. Ticks must attach for 36–48 hours to transmit the infection effectively.

Epidemiology

  • Regions:
    • U.S.: Northeastern, North-Central, and Pacific coastal regions.
    • Europe: Central and Eastern Europe.
  • Seasonality: Late spring and summer (tick nymph stage is most active).
  • Risk Factors:
    • Outdoor activities in endemic areas.
    • Contact with forested or grassy areas.
    • Inadequate use of protective clothing or repellents.

Pathophysiology

  • After a tick bite, Borrelia burgdorferi spreads locally in the skin, causing the characteristic erythema migrans (EM) rash.
  • The spirochetes disseminate hematogenously, leading to systemic involvement:
    • Immune Response: Triggered by spirochetal antigens, resulting in inflammation and tissue damage.
  • Persistent infection and immune-mediated damage are central to chronic manifestations.

Clinical Manifestations

Stage 1: Early Localized Disease (3–30 days post-bite):

  • Erythema migrans (classic bull’s-eye rash).
  • Flu-like symptoms: Fever, fatigue, malaise, myalgia, headache.

Stage 2: Early Disseminated Disease (weeks to months):

  • Fatigue: persistent fatigue is a hallmark of untreated disseminated Lyme disease 
  • Neurologic: Cranial nerve palsies (especially CN VII), meningitis, radiculopathy, headaches, depression dementia, painful peripheral radiculopathy 
  • Cardiac: Conduction system abnormalities, myocarditis, pericarditis, Atrioventricular blockade (the most common cardiac manifestation)
  • Multiple erythema migrans lesions.

3.Late Disease (months to years):

  • Arthritis: Joints: Asymmetric oligoarticular arthritis of the large joints, particularly the knees; Migratory pains in muscles, joints, and periarticular structures.  
  • Chronic neurologic symptoms: Encephalopathy, polyneuropathy, chronic insomnia, leukoencephalopathy.

Diagnosis

1.Clinical:

  • The diagnosis of early Lyme disease is clinical (History of tick exposure and presence of erythema migrans ) and does not require laboratory confirmation.

2.Laboratory:

  • Serology: Two-tier testing (ELISA followed by confirmatory Western blot).
  • PCR for Borrelia DNA in synovial fluid for Lyme arthritis.
  • ECG and echocardiography for Lyme carditis.

3.Differential Diagnosis:

  • Southern tick-associated rash illness (STARI), cellulitis, viral meningitis, rheumatoid arthritis.

Treatment

  1. Early Disease:
    • Doxycycline (first-line): 10–21 days.
    • Alternatives: Amoxicillin, cefuroxime, azithromycin.
  2. Neurologic or Cardiac Involvement:
    • IV ceftriaxone or cefotaxime for severe disease.
  3. Late Disease:
    • Lyme arthritis: Oral doxycycline or amoxicillin for 28 days; IV antibiotics for persistent symptoms.
  4. Prophylaxis:
    • Single-dose doxycycline if a tick bite meets specific criteria (e.g., Ixodes tick attached >36 hours, endemic area).
  5. Acrodermatitis chronicum atrophicans: doxycycline, amoxicillin, cefuroxime 

Prognosis

  • Good with Early Treatment: Most patients recover completely.
  • Delayed or Inadequate Treatment: Risk of chronic complications like arthritis or neurologic sequelae.
  • Post-Treatment Lyme Disease Syndrome (PTLDS): Persistent fatigue, pain, or cognitive symptoms despite eradication of infection.

SUPERPoint

Lyme disease, caused by Borrelia burgdorferi and transmitted by Ixodes ticks, manifests in stages ranging from erythema migrans to systemic involvement (neurologic, cardiac, and arthritis), with prompt diagnosis and antibiotic treatment essential for preventing chronic complications.

SUPERFormula

Tick bite in endemic area + Bull’s eye rash, Erythema migrans + Cranial nerve palsy (e.g., facial palsy) + AV block + Migratory arthritis + treat with doxycycline or IV ceftriaxone for severe cases) = Lyme Disease 

chronic fatigue + knee arthritis +  Atrioventricular block on ECG + History of a tick bite = Lyme disease