Urticaria

Basics

Description

• Cutaneous lesion with edema of epidermis and/or dermis
• Presents with rapid onset and pruritus; resolves within 24 hours
• Mast cell degranulation and histamine release are the main pathophysiological processes
• Angioedema may occur: nonpitting, erythematous, and takes up to 72 hours to remit
• Classification:
  • Acute: <6 weeks
  • Chronic: >6 weeks
  • Causal types: IgE mediated, non-IgE immunologically mediated, nonimmunologic

Synonyms

• Hives, Wheals

Epidemiology

• All ages affected; female > male (2:1 in chronic urticaria)
• Chronic urticaria >10 years in 20%
• Prevalence: 5–25%
• 3% have chronic idiopathic urticaria

Etiology and Pathophysiology

• Mediators: Histamine, cytokines, leukotrienes, proteases
• Site-specific effects:
  • Dermis: Urticaria
  • Deep dermis: Angioedema

Triggers

• Acute spontaneous urticaria: infections, foods, drugs, contact allergens, insect bites, transfusions
• Chronic spontaneous urticaria (CSU): infections, autoimmunity, thyroid disease, medications
• Chronic inducible urticaria (CIU):
  • Dermatographism
  • Cold urticaria
  • Delayed pressure urticaria
  • Solar/heat/vibratory/cholinergic/adrenergic/contact/aquagenic urticaria

Genetics

• No consistent pattern; HLA-DR4, HLA-DQ8 associations

General Prevention

• Avoid triggers

Associated Conditions

• Angioedema, Anaphylaxis

Diagnosis

History

• Rapid onset, pruritus, lesion resolution <24 hr
• Rule out anaphylaxis

Physical Exam

• Polymorphic plaques, central pallor, edema, erythematous halos
• Check for thyroid nodules, fever, infection signs

Differential Diagnosis

• Anaphylaxis, vasculitis, mastocytosis, pemphigoid, arthropod bites, SLE, contact dermatitis

Tests & Interpretation

• Acute: Usually clinical
• Chronic:
  • Initial: CBC, ESR, CRP, TFTs, LFTs, urinalysis, allergy testing
  • Special: ANA, RF, complement levels, cryoglobulins, H. pylori, stool for O&P
  • Procedures:
    • Challenge tests (e.g., ice cube test, exercise)
    • Skin biopsy if lesion >24 hr

Treatment

General Measures

• Avoid known triggers

Medication

• 1st-line: 2nd-gen H1 blockers:
  • Fexofenadine, loratadine, desloratadine, cetirizine, levocetirizine, rupatadine
• 2nd-line:
  • Increase dose of 2nd-gen H1s
  • Add 1st-gen H1s for nighttime pruritus
  • H2 blockers if needed

Special Populations

• Geriatrics: Use caution with 1st-gen due to sedation and anticholinergic effects

Referral & Inpatient Care

• Refer to allergist/dermatologist for refractory cases or lesions >24 hr
• Educate on EpiPen for potential airway compromise

Ongoing Care

Follow-Up

• Reassess in 6 weeks for persistent symptoms

Monitoring Tools

• UAS7, UCT (Urticaria Control Test)

Prognosis

• Acute: 70% resolve <72 hr
• Chronic: 35% resolve in 1 yr; 30% improve

Clinical Pearls

• Mainstay: Avoid triggers, treat with antihistamines
• Lesions >24 hr? Consider vasculitis
• Educate about anaphylaxis risk in urticaria

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