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Lyme disease - Management
What else might it be?

  • Tick bite hypersensitivity reaction
    • An erythematous skin lesion presenting while the tick is still attached or which has developed within 48 hours of detachment is most likely to be a tick bite hypersensitivity reaction rather than erythema migrans.
    • Tick bite hypersensitivity reactions are usually less than 5 cm in diameter, and itchy; they sometimes have an urticarial appearance, and typically begin to disappear within 24–48 hours.
  • Hypersensitivity to an insect bite — develops rapidly, is often itchy, and is usually smaller than erythema migrans (see the CKS topic on Insect bites and stings).
  • Other skin conditions to consider include:
    • Adverse reaction to a drug — presents as a deep, violaceous plaque. There is no change in size, and it is itchy and often on hands, feet, face, or genitals.
    • Bacterial cellulitis — usually occurs on a limb or at site of skin trauma. It presents as uniform erythema (redness), which is warm to touch and painful, and has a faster onset than erythema migrans (see the CKS topic on Cellulitis - acute). It may be present at the same time as erythema migrans.
    • Contact dermatitis — the shape or location often suggests the diagnosis; it is often vesicular (see the CKS topic on Dermatitis - contact).
    • Discoid eczema — is very itchy and scaly (see the CKS topic on Eczema - atopic).
    • Erythema annulare centrifugum — a small, pink papule that slowly enlarges to form a ring with a central clearing. It may be solitary or (more often) multiple, is smooth or slightly scaly at the advancing edge, and is rarely vesicular.
    • Erythema multiforme — appears as multiple target lesions (sometimes blisters). The lesions are small (less than 2 cm in diameter), diffuse, and symmetrical, with slow enlargement; palmar and mucosal involvement is common and there is often an obvious precipitant.
    • Granuloma annulare — is usually smaller than erythema migrans. The periphery is usually papular, and it can have a central clearing.
    • Pityriasis rosea — appears as multiple oval lesions, with peripheral scale and moderate itch; a herald patch on the trunk precedes other lesions by 7–14 days.
    • Southern tick-associated rash illness (STARI) — is a similar rash to erythema migrans, and is seen in southern US.
    • Spider bite (usually non-UK) — is often necrotic and very painful.
    • Tinea (ringworm) — these lesions are characterized by scale and itch (see the CKS topic on Fungal skin infection - body and groin).
    • Urticaria — the multiple raised lesions are nettle-like or blotchy, and very itchy; it usually resolves within 24–36 hours (see the CKS topic on Urticaria).

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