Urticaria Summary

Definition

  • Superficial skin swelling (epidermis/mucous membranes)
  • Red, raised rash with intense itching
  • Mast cell-driven disease

Acute vs Chronic

  • Acute: Self-limiting, <6 weeks
  • Chronic: Persistent, ≥6 weeks
  • Children: Usually viral-induced

Common Triggers

  • Viral infections (children)
  • Foods (nuts, shellfish, milk, eggs)
  • Drugs (NSAIDs, penicillin)
  • Insect bites/stings
  • Physical stimuli (CINDU)

First-line Treatment

  • Non-sedating antihistamines:
  • Cetirizine, fexofenadine, loratadine
  • Continue up to 6 weeks
  • Avoid sedating antihistamines

Severe Cases

  • Add short course oral corticosteroids
  • Prednisolone 40mg daily ≤7 days
  • Identify/manage underlying causes

Chronic Urticaria Types

  • CSU: Chronic Spontaneous (no external cause)
  • AU: Autoimmune (30-50% of chronic cases)
  • CINDU: Inducible (physical triggers)

Clinical Pearls

  • Children: Usually viral-induced
  • Chronic cases need specialist referral
  • Consider autoimmune screening
  • Mild cases may not need treatment

Urticaria

Definition

Superficial swelling of the skin (epidermis and mucous membranes) resulting in:

  • Red, raised rash (initially with pale center)
  • Intensely itchy

Pathophysiology

Mast cell-driven disease: Release of histamine and other inflammatory mediators (leukotrienes, prostaglandins) causes:

  • Pruritus (itching)
  • Vascular permeability → plasma leakage
  • Edema (swelling)

Causes

Acute Urticaria

  • Usually self-limiting, one-off episode
  • Common triggers:
    • Acute viral infections (especially in children)
    • Allergic reactions to:
      • Foods (nuts, shellfish, milk, eggs)
      • Insect bites/stings
      • Latex
      • Drugs (NSAIDs, penicillin, vaccines)

Chronic Urticaria (≥6 weeks)

  • Chronic Spontaneous Urticaria (CSU):
    • No identifiable external cause
    • Aggravated by heat, stress, NSAIDs, infections
  • Autoimmune Urticaria (AU):
    • 30-50% of chronic cases
    • IgG autoantibodies to FcεRI
    • Associated with autoimmune conditions (e.g., thyroiditis)
  • Chronic Inducible Urticaria (CINDU):
    • Triggered by physical stimuli

Emergency Department Management

  1. Identify and manage underlying causes/triggers where possible
  2. Mild urticaria with avoidable trigger:
    • Advise condition is likely self-limiting
    • May not require treatment
  3. Symptomatic treatment:
    • First-line: Non-sedating antihistamines
      • Cetirizine, fexofenadine, or loratadine
      • Continue for up to 6 weeks (clinical judgement)
    • Severe cases: Add short course oral corticosteroids
      • e.g., Prednisolone 40mg daily for ≤7 days

Clinical Pearls

  • Acute urticaria in children is most commonly viral-induced
  • Chronic urticaria often requires specialist referral
  • Autoimmune screening (e.g., thyroid function) may be warranted in chronic cases
  • Sedating antihistamines (e.g., diphenhydramine) should generally be avoided