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Clinical investigations from the RACP

Investigating the child with urticaria

David Bannister

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Abstract

Urticaria is common in children: 15 to 20% have at least one episode by adolescence. It is a result of transient extravasation of plasma into the dermis, which causes changes in the skin. Involvement in the upper dermis results in wheal formation, and localised vasodilatation produces redness.

Key Points

  • Allergy testing with skin prick testing or radioallergosorbent testing (RAST) is helpful only if there is strong suspicion of immediate urticaria.
  • Urticaria can have varying appearances, including wheals and erythema with circles or polycyclic borders on the trunk, limbs or face.
  • Persistent purple discolouration or purpuric centres may be a vasculitis.
  • The physical urticarias (triggered by changes with pressure, heat, water, cold, sunlight or exercise) are non-IgE mediated.
  • The commonest form of childhood urticaria is acute, self-limiting and non-IgE mediated and is usually due to viral infections with or without drug intake.
  • Urticaria associated with atopic dermatitis and angio-oedema of the lips may be due to foods.

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