What is the appropriate treatment for a patient with elevated CRP and fever, and an equivocal Lyme disease test result?

Treatment for Patient with Elevated CRP, Fever, and Equivocal Lyme Disease Test

Doxycycline is the treatment of choice for this patient with fever, elevated CRP, and equivocal Lyme disease test, as it effectively treats both Lyme disease and potential tick-borne coinfections like anaplasmosis that may be causing these symptoms. 1

Clinical Assessment and Diagnostic Considerations

When evaluating a patient with fever, elevated CRP (51), and equivocal Lyme test results, consider:

• The combination of fever and elevated inflammatory markers with equivocal Lyme serology suggests possible:

  • Early Lyme disease with developing antibody response
  • Coinfection with another tick-borne pathogen
  • Alternative infectious process

• Key considerations:

  • High-grade fever persisting >48 hours is atypical for uncomplicated Lyme disease alone 1
  • Elevated inflammatory markers (CRP 51) suggest active inflammatory process
  • Equivocal Lyme test may represent early infection before full seroconversion

Treatment Algorithm

First-line Treatment:

• Doxycycline 100 mg twice daily orally for 10-14 days 1, 2
  • Covers Lyme disease (Borrelia burgdorferi)
  • Effectively treats potential coinfections including Human Granulocytic Anaplasmosis (HGA)
  • Addresses the possibility that high fever may represent anaplasmosis coinfection

For patients who cannot take doxycycline (pregnancy, age <8 years, allergy):

• Amoxicillin 500 mg three times daily for 14 days 2
  • Note: If anaplasmosis is strongly suspected in doxycycline-contraindicated patients, add rifampin 300 mg twice daily for 7-10 days 1

For patients with neurologic involvement:

• Ceftriaxone 2 g IV daily for 14 days (range 10-28 days) 1, 2

Rationale for Doxycycline as First Choice

1. Covers multiple pathogens: The Infectious Diseases Society of America (IDSA) recommends doxycycline as the drug of choice for both Lyme disease and anaplasmosis 1

2. Addresses coinfection risk: High fever with elevated inflammatory markers in a patient with equivocal Lyme test should raise suspicion for coinfection with anaplasmosis, which requires doxycycline 1

3. Rapid response expected: Fever typically subsides within 24-48 hours after doxycycline treatment in tick-borne rickettsial diseases; failure to respond within this timeframe suggests alternative diagnosis 1

4. Evidence-based efficacy: Clinical trials have demonstrated that doxycycline is as effective as other antibiotics for Lyme disease, with no benefit to extended treatment durations 3

Important Clinical Pearls

• Monitor response closely: If fever persists >48 hours after starting doxycycline, reconsider diagnosis 1

• Avoid common pitfalls:

  • Do not wait for definitive Lyme serology before initiating treatment when clinical suspicion is high
  • Do not extend antibiotic duration beyond recommended course without clear evidence of treatment failure
  • Do not assume persistent symptoms after appropriate therapy represent ongoing infection 1, 2

• Laboratory considerations:

  • Consider testing for anaplasmosis (blood smear for intracellular inclusions, PCR, or serology)
  • Repeat Lyme serology in 2-4 weeks if initial test is equivocal
  • Blood cultures if alternative infection is suspected

• Tooth staining concerns: Limited courses of doxycycline in children have minimal risk of permanent tooth discoloration; benefit outweighs risk in serious tick-borne illness 1

• Treatment failure is rare: Studies show high success rates (>90%) with standard treatment courses for early Lyme disease 3, 4