Lyme disease (Lyme borreliosis) is a systemic, tick-borne infection caused primarily by the spirochete Borrelia burgdorferi (and less commonly Borrelia mayonii in North America). As the most common vector-borne illness in the United States, its clinical manifestations evolve through distinct stages affecting the skin, nervous system, heart, and musculoskeletal joints.
Core Vector Transmission & Post-Exposure Prophylaxis
- Primary Vector: Transmitted via the bite of infected Ixodes species ticks (Ixodes scapularis in the Northeast/Upper Midwest; Ixodes pacificus on the West Coast).
- Transmission Window: Bacterial transmission requires an infected tick to remain attached and feed for at least 24 to 36 hours (typically >36–48 hours). Unengorged ticks removed within 24 hours carry negligible risk.
- Post-Exposure Prophylaxis (PEP) Criteria: A single oral dose of Doxycycline 200 mg (in adults or children of any age) effectively prevents disease if ALL of the following criteria are met:
- Attached tick is identified as an Ixodes species and is engorged (attached ≥36 hours).
- Prophylaxis can be started within 72 hours of tick removal.
- Exposure occurred in a highly endemic area (≥20% local tick infection rate).
- Doxycycline is not contraindicated (e.g., severe allergy).
1. Clinical Presentation by Staging
| Clinical Stage | Characteristic Features & Organ Systems | Key Clinical Pearls & Red Flags |
|---|---|---|
| Stage 1: Early Localized (Days to Weeks post-bite) |
• Erythema Migrans (EM): Expandable annular rash expanding over days to ≥5 cm, often exhibiting a “bulls-eye” central clearing. • Non-pruritic, non-painful. • Flu-like symptoms (fatigue, fever, chills, myalgias, arthralgias, headache). |
• Clinical diagnosis alone is sufficient; serology is frequently falsely negative at this stage. • Un-treated EM self-resolves within 3–4 weeks, but infection progresses to late stages. |
| Stage 2: Early Disseminated (Weeks to Months post-bite) |
• Neurologic: Unilateral or bilateral Cranial Nerve VII Palsy (Bell’s Palsy), lymphocytic aseptic meningitis, painful radiculoneuritis. • Cardiac: Lyme Carditis (variable AV heart block, myopericarditis). • Dermatologic: Multiple secondary EM skin lesions. |
• Bilateral Bell’s Palsy is highly pathognomonic for Lyme disease. • Symptomatic AV block requires inpatient monitoring and IV antibiotic therapy. |
| Stage 3: Late Persistent (Months to Years post-bite) |
• Musculoskeletal: Oligoarticular inflammatory arthritis affecting large joints (knee is classic) with marked effusion. • Neurologic: Lyme encephalopathy (subtle memory/cognitive decline), peripheral neuropathy, fatigue. |
• Joint fluid aspiration reveals inflammatory synovial fluid (~25,000–50,000 WBCs/mcL). • Can cause permanent structural joint damage if left untreated. |
2. Diagnostic Approach & Serological Kinetics
| Testing Phase | Methodology | Serological Kinetics & Interpretation |
|---|---|---|
| Step 1: Screening Assay | Enzyme-Linked Immunosorbent Assay (ELISA) or Immunofluorescence Assay (IFA) | High sensitivity. If negative, no further testing is needed (unless patient is in early Stage 1, where clinical diagnosis suffices). If positive or equivocal, proceed to Step 2. |
| Step 2: Confirmatory Assay | Western Blot (IgM and IgG) OR Second Immunoassay (Modified Two-Tiered Testing) |
• Symptoms <30 days: Interpret both IgM and IgG Western Blot. • Symptoms >30 days: Interpret IgG Western Blot ONLY (IgM alone yields high false-positive rates after 1 month). |
| Antibody Kinetics | IgM & IgG Temporal Windows |
• IgM: Peaks at 2–4 weeks post-onset; declines within 4–6 months. • IgG: Peaks at 6–8 weeks; may persist indefinitely (years) at low levels despite effective cure (does NOT signify active infection). |
Diagnostic Pitfalls & Pearls
- Do NOT Test Early Localized Lyme: Serologic testing during the first 2–3 weeks of infection has a high false-negative rate (>50%). Patients presenting with classic Erythema Migrans should be diagnosed and treated empirically without lab testing.
- Routine Lab Non-Utility: Complete Blood Count (CBC) and routine chemistry panels are usually unremarkable and non-diagnostic.
- IgG Persistence: Seropositivity (IgG) alone after successful treatment does not indicate active infection or treatment failure. Test of cure is not recommended.
3. Treatment Protocols by Clinical Manifestation
| Clinical Manifestation | First-Line Antibiotic Regimens | Duration & Practice Considerations |
|---|---|---|
| Post-Exposure Prophylaxis | Doxycycline: Single oral dose of 200 mg. | Must be given within 72 hours of removing an engorged tick attached ≥36 hours in an endemic zone. Observation is appropriate if criteria are not met. |
| Early Localized (EM) & Mild Disseminated |
• Doxycycline: 100 mg BID • Amoxicillin: 500 mg TID • Cefuroxime axetil: 500 mg BID |
14-day duration (range 10–14 days). Doxycycline is preferred due to co-coverage for Anaplasma phagocytophilum. Amoxicillin or Cefuroxime preferred in pregnant/lactating patients. |
| Isolated Facial Palsy (CN VII) | Oral Doxycycline: 100 mg BID | 14 to 21-day duration. Corticosteroids are generally avoided unless severe facial paralysis occurs, in which case short-course steroids may be combined with antibiotics. |
| Lyme Carditis / Meningitis / Severe Neurologic | IV Ceftriaxone: 2 g IV daily (Alt: IV Cefotaxime or High-dose Oral Doxycycline if stable) |
14 to 21-day duration. Inpatients with symptomatic AV heart block (1st degree with PR >300 ms, 2nd, or 3rd-degree block) require continuous telemetry until block resolves. |
| Lyme Arthritis (Stage 3) | Oral Doxycycline, Amoxicillin, or Cefuroxime | 28-day duration. If arthritis persists after a single 28-day oral course, a second 28-day oral course or a 14-day course of IV Ceftriaxone is indicated. |
High-Yield Exam & Practice Pearls
- Tick Attachment Window: An attached tick must feed for ≥24–36 hours to transmit Borrelia burgdorferi.
- PEP Doxycycline Safety in Pediatrics: Short-course doxycycline (up to 21 days) is safe for children of all ages without risking tooth discoloration.
- CN VII Palsy Differential: Bilateral facial nerve palsy is classic for Lyme disease (other causes: Sarcoidosis, Guillain-Barré Syndrome, HIV).
- Early Stage Clinical Diagnosis: Erythema Migrans = Immediate treatment. Do NOT order serology for early localized disease.
- Two-Tiered Rule: Never order a Western Blot without a preceding positive/equivocal ELISA screen. IgM Western Blot is only valid if symptoms are present for <30 days.
- Prevention Essentials: Standard tick protection includes permethrin-treated clothing, DEET insect repellent, daily body checks, and immediate prompt tick removal using fine-tipped tweezers by pulling straight up.
