Updated: 2/27/2022

Lyme Disease

Review Topic
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  • summary
    • Lyme Disease is a systemic infection caused by tick-born B. burgdorferi which usually presents with flu-like symptoms, a characteristic rash, and occasionally acute joint effusions.
    • Diagnosis is confirmed by a history of travel to a tick-heavy regions, presence of erythema migrans rash, and a positive lyme titers on an ELISA test.
    • Treatment is usually oral doxycycline for acute or mild disease.
  • Epidemiology
    • Incidence
      • most common tick-borne illness in the US
      • 19,931 cases in 2006
      • most cases occur in June, July, and August
    • Demographics
      • bimodal age distribution
        • children 5-9 (8.6 cases/100,000)
        • adults 55-59 (7.8 cases/100,00)
      • geographic locations
        • northeast, midwest, western US (areas with heavy deer population)
        • Maryland to Maine (Ixodes scapularis)
        • Great Lakes region (Ixodes scapularis)
        • Pacific Northwest (Ixodes pacificus)
  • Etiology
    • Pathophysiology
      • mechanism of transmission
        • zoonotic - transmitted from nonhuman animals to humans
          • mice, squirrels, shrews, and other small mammals are carriers of B burgdorferi
          • Ixodes tick feeds on these small animals and spirochete is carried in its gut
          • humans become infected when bacteria is injected into the skin as ticks attach to feed
            • transmission takes 48-72 hours
      • pathophysiology
        • caused by B burgdorferi
        • tick saliva with spirochete disrupt local immune mechanisms
        • create a protective environment and the bacteria replicate
        • spirochetes multiply and expand within the dermis, causing erythema migrans
          • rash caused by the host inflammatory response
        • the spirochete then undergoes hematogenous dissemination to multiple sites
          • skin
          • central nervous system
          • joints
            • induces an inflammatory response
              • synovial hypertrophy
              • vascular proliferation
              • infiltration of mononuclear cells
              • immune complexes accumulate in synovial fluid
      • pathobiology
        • B burgdorferi induces chondrocytes to produce matrix metalloproteinases
          • causes degradation of extracellular matrix proteins, collagen, and proteoglycans
          • may contribute to cartilage damage
  • Classification
    • Stage 1 (rash) - early localized
      • 1 to 30 days after bite
      • erythema migrans (bull's-eye rash) is hallmark
      • rash may be found on head, neck, arms, legs, back, abdomen, axilla, groin, and chest
      • flu-like symptoms
        • fatigue
        • headache
        • malaise
    • Stage 2 (neurologic and cardiac) - early disseminated
      • weeks to months after bite
      • progresses to stage 2 in 15-20% of untreated patients
      • neurologic symptoms
        • CN VI palsy
        • CN VII palsy
        • lymphocytic meningitis
        • migratory polyarthritis or monoarthritis, tendonitis, bursitis
      • Lyme carditis relatively rare
        • may have a cardiac conduction abnormality
        • symptoms
          • syncope
          • fatigue
          • dizziness
          • shortness of breath
          • palpitation
      • prognosis good with complete resolution following treatment
    • Stage 3 (arthritis) - late
      • months to years after bite
      • occurs in 60% of untreated patients
      • arthritis (usually the knee)
        • swelling disproportionate to tenderness
        • intermittent arthritis
        • chronic monoarthritis
      • acrodermatitis chronica atrophicans
  • Presentation
    • History
      • tick bite in May through November
    • Symptoms
      • fever, headache, myalgia, arthralgia, fatigue
      • neurologic symptoms
        • headache, neck stiffness, encephalitis
        • facial CN VII palsy
          • bilateral in 50% (unlike Bell's palsy)
        • polyradiculoneuropathy
          • numbness, paresthesia, weakness, cramps
      • carditis (complete heart block)
      • acute joint pain
      • acute or chronic arthritis
    • Physical exam
      • erythema migrans ("bullseye rash") in 60-80% of patients
        • expanding rash >5cm diameter 1 to 3 weeks after tick bite
        • itching or burning
        • fades after 1 month
        • at axillary or gluteal folds, hairline, near elastic bands (bra strap or underwear)
      • acute, self limiting joint effusions
        • knee and shoulder
        • recurrent
      • acrodermatitis chronica atrophicans
        • "cigarette paper" skin
        • dorsum of hands, feet, knees, elbows
        • in older patients
  • Studies
    • Serum labs
      • WBC normal or elevated
      • ESR, CRP elevated
    • ELISA (sensitive, not specific)
      • 2 steps
        • if ELISA positive, proceed to Western blot (specific)
      • seroconversion takes weeks to become positive
      • prior Lyme disease might have persistently positive results
      • vaccination gives positive ELISA, negative Western blot
    • CSF (patients with polyradiculitis and CN VII neuropathy)
      • increased protein
      • lymphocytic pleocytosis
    • Joint aspiration / Synovial fluid
      • 10,000-25,000 WBC/mm3
        • lower than baterial septic arthritis
      • PMN predominance
    • Skin biopsy culture
      • Culture on Barbour-Stoenner-Kelly medium
      • use skin edge punch biopsy from erythema migrans lesion
    • PCR
  • Differential
    • Bacterial septic arthritis
      • features that differentiate Lyme's diseae from bacterial septic arthritis include
        • ability to bear weight
        • normal serum WBC
        • lower synovial fluid WBC count
  • Treatment
    • Non-operative
      • oral antibiotics for mild disease
        • indications
          • in endemic regions, if erythema migrans is present, start antibiotics without blood tests
        • medications
          • adults
            • doxycycline (not in children <8 years) x 10 days
            • amoxicillin
            • cefuroxime
          • children (<8-years-old)
            • amoxicillin
            • cefuroxime
      • IV antibiotics
        • indications
          • arthritis and neurologic involvement
          • patients whose symptoms are unchanged after oral therapy
        • medications
          • IV ceftriaxone or cefotaxime
          • IV penicillin G
    • Operative
      • synovectomy
        • indications
          • chronic arthritis not responding to IV antibiotics
  • Complications
    • Persistent joint pain
      • may have a slightly increased incidence of persistent joint swelling despite therapy
    • Chronic Lyme disease
      • disabling musculoskeletal pain
      • neurocognitive symptoms
      • fatigue
    • Chronic arthritis
      • rare

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(OBQ12.211) A 13-year-old boy presents to the emergency department in Rhode Island with knee pain for three days duration. It was atraumatic in onset. He has been afebrile. Upon physical examination, he is noted to have a tense, swollen knee and the skin lesion seen in Figure A. An oral course of antibiotics is selected as definitive management. What antibiotic would be most appropriate for this patient, and what is its primary mechanism of action?

QID: 4571

Doxycycline, Inhibits the 50s ribosomal subunit



Doxycycline, Inhibits the 30s ribosomal subunit



Cephalexin, Blocks cell wall synthesis



Cephalexin, Folic acid inhibitor



Rifampin, RNA synthesis inhibitor



L 4 C

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