Urticaria


  • Pruritic, elevated skin lesions surrounded by erythematous base commonly described as "hives"
    Due to transient extravasation of plasma into the dermis. It is a common condition - 25% of individuals will have it at some stage.

    Deeper subcutaneous extension is much less common and termed angioedema. It involves face (eyelids, lips, tongue), hands and feet, and sometimes other areas ( trunk, genitalia, mucous membranes ).

    Acute Urticaria ( <6 weeks) Chronic Urticaria (>6 weeks)

    Assessment

    Explore events a few hours or days before onset of rash.

    A specific cause is not identified in most of the cases (Idiopathic)

    Other causes are

    • Medications including antibiotics like penicillin, cefaclor (5-21 days after commencing course),amoxycillin,etc
    • Infections include viruses and bacteria
    • Foods are infrequent causes (may include nuts, eggs, shellfish, strawberries, tomatoes, and cow's milk.)
    • Bites and stings include bees, wasps, scorpions, jelly fish and spiders.
    • Physical triggers may include pressure, cold, exercise and rarely water.

    Physical examination:

    Erythematous raised skin lesion (Wheal)

    • Localised or generalised
    • Well circumscribed but often coalescent
    • May be intensely pruritic with excoriation
    • Vary in size from tiny flat papules to large raised plaques
    • Flat centre with raised erythematous edge
    • Diagnostic feature is polymorphic appearance and transience of individual lesion.
    • Observe for dyspnoea or dysphagia the first few hours after urticaria

    Anaphylaxis is a medical emergency - sudden onset of urticaria, angioedema, dyspnoea or hypotension . Treat immediately

    If recurrent angioedema without wheals, think of  C1 esterase inhibitor deficiency .

    urticaria pic 1

    Blotchy rash typical of urticaria

    urticaria pic2

    Urticarial lesions with typical clear skin in centre. These are not "target lesions"

    Differential diagnosis of urticaria

    Erythema multiforme

    How to distinguish? EM is:

    • Usually not itchy
    • Does not move around - individual lesions perist for days
    • Has target lesions with a central papuler, blister, purpura or ulcer.
    • Often has mucosal involvement

    Rare differentials

    • Mastocytosis
    • Flushing
    • Juvenile Rheumatoid Arthritis
    • Vasculitis - Henoch Schonlein purpura
    • Pityriasis rosea (early lesions)

    Investigations

    Investigations are usually not indicated for acute urticaria

    Initial investigations of chronic urticaria include FBE, Differential, ESR and ANA.

    Management

    • Remove identifiable cause if any
    • Cool Compresses
    • Explanation, information and reassurance
    • Manipulation of diet is not indicated.
    • Anti-histamines to alleviate itching
    • Promethazine (Phenergan)
      0.2-0.5mg/kg/dose (adult 10-25mg) 6-8H IV, IM or oral.
      Contraindicated for children less than 2 years old
      or
      Cetirizine (Zyrtec) 0.2mg/kg/dose (adult 10mg) 12-24H oral.
      Contraindicated for children less than 1 year old
    • Steroid creams do not work. For severe cases, a single dose of oral prednisolone may be considered

    Indications for specialist referral:

    • associated bruising or systemic features (need to exclude urticarial vasculitis or chronic urticaria as a manifestation of another disease process)
    • Severe life-threatening allergy e.g. peanut or latex allergy
    • Poor response to antihistamines
    • Angioedema involving the airways
    • Chronic urticaria (>6 weeks)

    Resources

    Parent Information Sheet (HTML version)