erythema chronicum migricans (erythema migrans)

Etiology

• associated with early, localized Lyme disease (Borrelia burgdorferi)
• recurrent erythema migrans represents reinfection with a different genotype of Borrelia burgdorferi rather than relapse
• Southern tick-associated rash illness

Epidemiology

• 80% of patients with Lyme disease

Clinical manifestations

• lesion develops subsequent to & surrounding the site of a tick bite
• incubation period 5-14 days
• annular, sometimes urticarial, erythematous lesion with central clearing
  • 'bullseye' appearance
• lesions are single (75%) or multiple (25%)
• lesions > 5 cm in size
• lesions expand over days, resolve over weeks
• systemic symptoms common & may be only manifestation

* images

Laboratory

• no laboratory testing recommended
  • arguments for no testing in less than convincing
• Borrelia burgdorferi DNA from skin biopsy
• Borrelia burgdorferi serology may be negative in early, localized Lyme disease

Differential diagnosis

• tick bite reaction:
  • incubation period hours
  • size: < 1 cm
  • expands over hours, resolves over days
  • systemic symptoms rare
• Streptococcal cellulitis
  • progresses over hours
  • very tender
  • patients often very ill
• burn (history)
• fixed drug eruption (history)
• dermatophyte infection
  • less erythema
  • evolves more slowly than erythema migrans
  • raised active border with central clearing
• necrotic spider bite (endemic areas)
• nummular eczema

Management

• see Lyme disease
• empiric oral therapy 14-21 days, regardless of cause (however, it would seem prudent to determine the cause)
  • 1st line agents
    • doxycycline 100 mg PO BID
    • amoxicillin 500 mg PO TID
    • cefuroxime 500 mg PO BID
  • alternative agent: azithromycin 500 mg PO QD
  • intravenous ceftriaxone for cardiac or neurologic manifestations or evidence of disseminated Lyme disease

More general terms

• sign/symptom
• skin lesion

Additional terms

• Lyme disease