Urticaria

Question 1

Definition

Answer 1

• Erythematous, blanching, oedematous, non-painful, pruritic lesions that typically last less than 24 hours and leave no residual markings upon resolution. Episodes of less than 6 weeks are acute and over 6 weeks are chronic.

Question 2

Aetiology

Answer 2

• Most cases are allergic in nature and caused by an IgE-mediated reaction.
• Most common agents include:
  
  • Drugs (i.e. penicillins, cephalosporins)
  • Foods (i.e. milk, eggs, peanuts, shellfish)
• Non-IgE-mediated mechanisms tend to involve certain drugs (i.e. NSAIDs, opoids, vancomycin)
• Some cases are idiopathic

Question 3

Signs and symptoms

Answer 3

• Signs/symptoms include erythematous oedematous lesions, pruritis, resolution within 24 hours, swelling of face/tongue/lips and blanching lesions.
• Can be associated with angioedema and flushing.
• Risk factors include positive FHx, exposure to drug trigger, exposure to food trigger, recent viral infection and recent insect bite.

Question 4

Pathophysiology

Answer 4

• Mast cells are thought to be the primary effector cells which, when activated, degranulate and release vasoactive mediators such as histamine, leukotriene C4 and prostaglandin D2.
• Release of these mediators leads to vasodilation and increased vascular permeability.
• This manifests as oedema and pruritis.
• A second, delayed release of inflammatory cytokines (TNF, IL-4, IL-5) accounts for the inflammatory infiltrate and longer lasting lesions.
• Urticaria is confined to the dermal layer whereas angioedema involves deeper sub-dermal layers.

Question 5

Investigation

Answer 5

• FBC
  
  • Normal or abnormal
• Metabolic panel
  
  • Normal or abnormal
• Urinalysis
  
  • Proteinuria
  • Bacteriuria
• ESR
  
  • Elevated
• CRP
  
  • Elevated
• Anti-IgE receptor antibody
  
  • Positive
• Skin biopsy
  
  • Urticarial vasculitis

Question 6

Treatment

Answer 6

• Airway protection (add adrenaline if airway involvement)
• H1 receptor antagonists (i.e. fexofenadine)
• IV corticosteroids
• Trigger identification and avoidance

Question 7

Complications

Answer 7

• Excoriations
• Sedation
• Skin infections

Question 8

Prevention and prognosis

Answer 8

• Secondary prevention
  
  • Avoid triggers
• Prognosis
  
  • Excellent prognosis but worse in chronic cases