Lyme Disease
A tick-borne bacterial infection that starts with a bullseye rash and can spread to cause severe joint pain, facial paralysis, and heart block if left untreated.
Emergency Management: Lyme Carditis causing complete heart block: Requires immediate telemetry admission, IV Ceftriaxone, and often insertion of a temporary transvenous pacemaker until the block resolves (usually in 1-2 weeks).
Lyme disease is the most common vector-borne illness in North America and Europe, caused by the spirochete bacteria Borrelia burgdorferi and transmitted by the bite of infected Ixodes ticks. It is a multisystem inflammatory disease affecting the skin, nervous system, heart, and joints.
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.
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.
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.
Early Localized/Disseminated (without severe neuro/cardiac): Doxycycline 100 mg PO BID for 10-14 days. Alternatives: Amoxicillin 500 mg PO TID or Cefuroxime 500 mg PO BID. Lyme Arthritis: Doxycycline 100 mg PO BID for 28 days.
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).
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.