Should a patient with a history of Lyme disease in 2006 be tested for Lyme disease again after a potential exposure about a month ago?

Diagnosis of Suspected Lyme Disease Reinfection

For a patient with a history of Lyme disease in 2006 who suspects reinfection one month ago, a thorough skin examination for erythema migrans (EM) is essential, as most reinfection cases will present with EM. If EM is absent, serologic testing with acute and convalescent samples is recommended to detect changes in antibody response. 1

Diagnostic Approach for Suspected Reinfection

Step 1: Clinical Assessment

• Perform detailed skin examination for erythema migrans (EM) rash
• Assess for symptoms such as:
  • Headache, arthralgia, fatigue
  • Fever and chills
  • Regional lymphadenopathy
  • Musculoskeletal pain

Step 2: Testing Decision Algorithm

1. If EM rash is present:

   • No serologic testing required
   • Proceed directly to treatment 1, 2

2. If no EM rash but high clinical suspicion:

   • Conduct two-tiered serologic testing:
     • First tier: ELISA or IFA
     • Second tier: Western immunoblot for confirmation 2
   • Consider acute and convalescent phase testing (3-4 weeks apart) to detect:
     • Increase in ELISA titer
     • Increase in number of antibody bands 1

Important Considerations

Antibody Persistence

• Antibodies from previous Lyme infection can persist for months to years after successful treatment 1, 2
• Persistent antibodies do not indicate active infection or treatment failure 2
• This persistence makes diagnosis of reinfection challenging when relying solely on serology 1

Interpretation of Results

• IgG Western blot requires ≥5 of 10 specific bands to be positive 2
• IgM Western blot requires ≥2 of 3 specific bands (21-24,39, and 41 kDa) 2
• Comparing acute and convalescent samples is more valuable than a single test for suspected reinfection 1

Common Pitfalls to Avoid

1. Relying solely on serology without clinical correlation:

   • Serologic testing alone cannot differentiate between active infection and antibody persistence from previous infection 2

2. Ignoring pretest probability:

   • Consider exposure history, geographic location, and season 1
   • False positives are more likely in low-prevalence areas 1

3. Misinterpreting persistent symptoms:

   • Some patients develop post-Lyme symptoms that are not responsive to antibiotics 2
   • Consider alternative diagnoses when symptoms persist beyond 6 months after treatment 2

Summary of Testing Recommendations

• With EM rash: No testing needed, treat empirically
• Without EM rash: Two-tiered serologic testing with comparison of acute and convalescent samples
• Interpret results cautiously: Consider antibody persistence from previous infection
• Focus on clinical changes: Look for evidence of increasing antibody response or new bands on Western blot

By following this approach, you can appropriately diagnose and manage potential Lyme disease reinfection while avoiding the pitfalls of serologic testing in patients with previous infection.