Urticaria

Snapshot

• A 25-year-old man presents with an itchy rash on his chest wall. He denies any exposures to insects and denies any previous allergies. He recently had an upper respiratory infection. Physical exam shows blanching, raised, edematous annular lesions that are well-circumscribed. Some lesions are coalesced. This is his first episode of this itchy rash. He denies any other symptoms.

Introduction

• Pruritic inflammation of the skin commonly known as “hives”
• Characterized by superficial, localized edema and erythema
• Epidemiology
  • most frequent dermatologic disorder seen in the emergency room
• Pathogenesis
  • involving dermis and epidermis
  • mast cell and basophil release of vasoactive substances
    • histamine, bradykinin, and prostaglandins
    • intense pruritus is from histamine in the dermis
  • type I hypersensitivity reaction 
• Triggers of acute urticarial (< 6 weeks)
  • drugs
  • food
  • viral infection
  • recent illness
  • insect bite
  • emotional stress
  • cold or heat
  • alcohol ingestion
  • pregnancy
  • exposure to other allergens (pet dander, dust, mold, or chemicals)
  • sun
• Chronic urticarial is usually idiopathic (> 6 weeks)
• Etiology identified in 40-60% of acute cases and 10-20% in chronic cases

Presentation

• Symptoms
  • history of previous urticaria
  • pruritus
  • lasts a few hours
  • resolves spontaneously
• Physical exam
  • well-circumscribed erythema and edema on skin
  • blanching, raised, and palpable wheals
  • can occur on anywhere on the body
  • dermotographism (urticaria from light scratching)
• indicates very sensitive skin

Evaluation

• Labs or biopsy not indicated for acute urticarial unless diagnosis is unclear
• ↑ IgE
• For chronic or recurrent urticarial
  • test ESR, TSH, and ANA
• Histology of lesion 
  • dermal edema 
• lymphatic channel dilation

Differential Diagnosis

• Hereditary angioedema 
• Contact dermatitis 
• Multiple insect bites
• Erythema multiforme 

Treatment

• If known, discontinue offending agent
• If concern for airway compromise
  • epinephrine
• Anti-histamines
• second generation > first generation

Prognosis, Prevention, and Complications

• Prognosis
  • most resolve spontaneously
• Prevention
  • avoid known triggers
  • take second generation anti-histamine daily
• Complications
  • life-threatening angioedema