Lyme Disease

Detailed Overview

The disease occurs in stages: early localized, early disseminated, and late disseminated. The hallmark of the early stage is the erythema migrans rash. If untreated, the spirochetes disseminate, causing neurologic (facial nerve palsy, meningitis), cardiac (AV block), and rheumatologic (Lyme arthritis) complications. Diagnosis is primarily clinical in the early stage and relies on two-tiered serologic testing in later stages. Most cases resolve completely with a course of oral antibiotics.

Epidemiology & Demographics

In the US, an estimated 476,000 cases occur annually, heavily concentrated in the Northeast, Mid-Atlantic, and Upper Midwest regions. Peak incidence is in late spring and summer. Bimodal age distribution: children 5-14 years and adults 45-55 years.

Etiological Mechanism

Caused by the spirochete Borrelia burgdorferi (and B. mayonii in the US). Transmitted by the blacklegged tick (Ixodes scapularis in the East/Midwest, Ixodes pacificus on the West Coast).

Primary Causes

Bite from an infected Ixodes tick that must be attached for at least 36-48 hours to transmit the bacteria.

• Geographic Location: Residing in or traveling to highly endemic areas (e.g., Connecticut, New York, Pennsylvania, Wisconsin).
• Outdoor Activities: Hiking, camping, or working in wooded or brushy areas with high grass.
• Exposed Skin: Not wearing protective clothing or using tick repellents.

Borrelia burgdorferi is injected into the skin via tick saliva. The spirochete expresses OspC protein, enabling it to evade early immune detection. It locally replicates, causing the expanding Erythema Migrans rash via a localized inflammatory response. It then disseminates hematogenously or through the lymphatics to target organs (heart, CNS, joints). Pathogenesis in these organs is largely driven by the host's robust immune response, specifically macrophages and T-cells reacting to spirochetal lipoproteins, causing severe localized inflammation rather than direct tissue destruction by toxins.

Characteristic Clinical Presentation

• Erythema Migrans: An expanding red, painless macule or papule that may clear in the center, forming a 'bullseye' target lesion. Appears 7-14 days post-bite.
• Severe Arthralgia/Arthritis: Swelling and intense pain, typically in large joints like the knee, occurring in late-stage disease.
• Neurologic Symptoms: Unilateral or bilateral facial droop (Bell's palsy), severe headache, and neck stiffness.

Physical Examination Signs

• Erythema migrans rash (> 5 cm diameter)
• Unilateral or bilateral facial nerve palsy (CN VII)
• Massive effusion of the knee joint without significant erythema or severe resting pain

• Third-Degree AV Block: Lyme carditis can cause rapid onset of complete heart block requiring temporary pacing.
• Post-Treatment Lyme Disease Syndrome (PTLDS): Persistent fatigue, pain, or cognitive difficulties lasting > 6 months after adequate antibiotic therapy.

Diagnostic Criteria & Guidelines

Early localized disease: Clinical diagnosis based entirely on the presence of Erythema Migrans; serology is often negative and not recommended. Later stages: Require Two-Tiered Testing Algorithm—Step 1: EIA or IFA for total Lyme antibodies. If positive/equivocal, Step 2: Western blot (IgM and IgG). Or the modified 2-EIA tier test.

Differential Diagnosis

• Cellulitis or Spider Bite (vs. EM rash)
• Idiopathic Bell's Palsy
• Septic Arthritis
• Viral Meningitis

Laboratory Tests & Biomarkers

• Two-Tiered Serology (ELISA + Western Blot): Positive (IgG requires 5/10 bands; IgM requires 2/3 bands).
• Synovial Fluid Analysis: Leukocyte count 10,000 to 25,000 /microL, predominantly neutrophils (Lyme arthritis PCR may be positive).
• ECG: Varying degrees of AV block in patients with Lyme carditis.

Imaging Modalities & Findings

• Joint Ultrasound: Large synovial effusion, particularly of the knee, without bone destruction.

• Early Localized (Days to 1 month)
  Erythema migrans rash at the bite site, accompanied by flu-like symptoms (fatigue, myalgia, fever).
• Early Disseminated (Weeks to months)
  Multiple EM lesions, neurologic involvement (meningitis, facial palsy), and cardiac involvement (atrioventricular heart block).
• Late Disseminated (Months to years)
  Lyme arthritis (mono- or oligoarticular large joint swelling) and subtle encephalopathy.

Second-Line & Adjunctive Therapy

For severe neurologic (meningitis) or severe cardiac (3rd-degree block) involvement: Ceftriaxone 2g IV daily for 14-21 days.

Surgical & Procedural Management

Arthroscopic synovectomy for antibiotic-refractory Lyme arthritis (persistent > 2 months after two courses of antibiotics).

Recommended Lifestyle Changes

• Tick checks after outdoor activities; shower within 2 hours of coming indoors.
• Use permethrin-treated clothing and DEET or Picaridin on exposed skin.

Patient Counseling & Advice

Advise that the tick must be attached for at least 36 hours to transmit disease, so prompt removal prevents infection. Explain that PTLDS is real but does not respond to prolonged (>4 weeks) IV antibiotics, which carry high risks.

Follow-Up & Monitoring Schedule

Clinical follow-up in 2-4 weeks to ensure rash and symptoms have resolved. Repeat serology is NOT recommended as IgG will remain positive for years, creating false alarm.

Preventive Strategies

Prophylaxis: A single dose of Doxycycline 200 mg PO can be given to adults if an engorged Ixodes tick was attached for >36 hours in a highly endemic area, given within 72 hours of removal.

Excellent. > 90% of patients are completely cured with a standard course of oral antibiotics. Mortality is extremely rare.