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Erythema Chronicum Migrans
Aka: Erythema Chronicum Migrans, Erythema Migrans
- See Also
- Lyme Disease
- Definition
- Pathognomonic bullseye rash of early Lyme Disease
- Epidemiology
- Now thought to occur in 90% of Lyme Disease cases
- Previously thought to be seen in only 50-60%
- Lower detection due to ECM rash that is missed
- Reinforces need for very careful skin exam
- Appears in 86-100% of symptomatic Lyme Disease cases
- Timing
- Occurs 3-30 days (median 7 days) after deer Tick Bite
- Distribution
- Localized rash at deer Tick Bite site
- Appearance
- Initial
- Small red painless Papule at Tick Bite site
- Rash does not itch
- Expands centrifugally over days or weeks
- Later: Annular Lesion
- Circular, oval or triangular
- Central clearing or darkening with induration (bullseye or target appearance)
- Occurs in only 19-33% of cases
- Macular, papular or vesicular
- Rapid and prolonged expansion (unique to Erythema Migrans)
- Expands to >5 cm diameter
- Typically 20-30 cm (up to 70 cm) diameter
- Contrast with Insect Bite reaction
- Resolution
- Rash resolves in weeks if not treated
- Variations
- Multiple lesions (hematogenous spread of infection) in 10-20% of cases
- Central vessicle or Pustules (5% of cases)
- May appear purpuric on legs
- Symptoms
- No Pruritus
- Differential Diagnosis
- See Annular Lesion
- Localized hypersensivity reaction to Insect Bite
- Typically <2.5 to 5 cm in size
- Course
- Onset while tick still attached
- Starts to resolve within 48 hours
- Distinguish from Erythema Migrans
- Mark margins
- Observe for 48 hours off antibiotics
- Improvement suggests not a Lyme Disease rash
- Contact Dermatitis
- Pruritus (does not occur in Erythema Migrans)
- Cellulitis
- Distribution may help distinguish from EM rash
- Cellulitis uncommon in typical eyrthema migrans sites: Axilla, popliteal fossa, Abdomen, back and groin
- Erythema Multiforme
- Multiple target lesions each typically <2 cm diameter
- Granuloma Annulare
- Scaling erythematous lesions with central clearing (esp. hands and feet)
- Methicillin Resistant Staphylococcus Aureus (MRSA)
- Lesions with necrotic central eschar
- Tinea Corporis
- Urticaria
- Interpretation: Classic Erythema Migrans rash
- Erythema Migrans is diagnostic for Lyme Disease
- Allows diagnosis without confirmatory testing
- Erythema Migrans is the only CDC-supported non-laboratory finding for definitive Lyme Disease diagnosis
- References
- Nadelman (1995) Am J Med 98:15S-24S [PubMed]
- Stanek (2003) Lancet 362:1639-47 [PubMed]
- Tibbles (2007) JAMA 297(23): 2617-27 [PubMed]
- Wormser (2006) Clin Infect Dis 43:1089-134 [PubMed]