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Lyme disease - Management
What are the features of erythema migrans?

  • Primary (or solitary) erythema migrans has the following features:
    • Appearance (see www.hpa.org.uk for a photo)
      • Round or oval in shape; pink, red, or purple in colour.
      • Usually flat, but a vesicle or pustule is present at the centre in 5% of people, and the border may be slightly raised.
      • There is often a central clearing or a target-like appearance (in 65–80% of people infected in Europe, but in only 20–35% of those infected in the US), or the lesion may be uniformly red (more common in the US).
    • Size
      • Usually expands over days to weeks.
      • Diameter is usually larger than 5 cm (median 16 cm), and can be as large as 1 metre.
    • Location
      • At the site of a tick bite. However, in Europe, only two thirds of people with erythema migrans recall the tick bite.
      • Often on the legs, at flexor creases (knees, axillae, and groins), around the waistband, under the breasts, near to straps (which impede the forward progress of ticks), or (particularly in children) at the hairline or the upper parts of the body.
    • Timing
      • Typically appears 7–10 days (range 3–36 days) after the tick has detached or was removed.
      • An erythematous skin lesion presenting while the tick is still attached or which develops within 48 hours of detachment is most likely to be a tick bite hypersensitivity reaction.
    • Associated symptoms
      • The rash may be mildly painful or itchy.
      • In Europe, around a third of people with erythema migrans experience flu-like symptoms, including fever, headache, tiredness, nausea, vomiting, arthralgia (joint pain), and myalgia (muscle pain). Flu-like symptoms are more common in the US.
      • Rarely, neurological features may also be present, but these usually occur later in the disease.
  • Secondary (or disseminated) erythema migrans may occur following haematogenous dissemination of infection, resulting in multiple lesions, usually smaller than 5 cm in diameter.
  • Erythema migrans may be confused with a number of other skin conditions — see Differential diagnosis.

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