Etiology of Urticaria Multiforme
Urticaria multiforme is primarily caused by hypersensitivity reactions, most commonly triggered by infections (particularly upper respiratory infections) and medications (especially antibiotics like amoxicillin). 1, 2
Clinical Characteristics and Differentiation
Urticaria multiforme is a distinct clinical variant of urticaria characterized by:
- Acute onset of large, annular, polycyclic erythematous wheals
- Dusky or ecchymotic centers giving a target-like appearance
- Associated acral and facial angioedema
- Positive dermatographism
- Primarily affects infants and young children
- Self-limiting course with favorable response to antihistamines
Key Etiologic Factors
1. Infectious Triggers
- Viral infections: Most common infectious cause in children 3
- Herpesviridae family infections (particularly in children)
- Upper respiratory tract infections
- Otitis media
2. Medication-Related Triggers
- Antibiotics: Particularly amoxicillin 2
- Other medications: Similar to triggers of ordinary urticaria 4
- NSAIDs and aspirin
- Codeine and other opiates
- Radiocontrast media
3. Non-Immunological Mechanisms
- Mast cell and basophil degranulation can occur independently of IgE receptor activation 4
- Medications like codeine and radiocontrast media can directly trigger degranulation
- NSAIDs and aspirin likely work through leukotriene formation and histamine release 4
Differential Diagnosis Considerations
Urticaria multiforme is frequently misdiagnosed as:
- Erythema multiforme
- Serum sickness-like reaction
- Urticarial vasculitis
- Acute hemorrhagic edema of infancy (AHOI syndrome) 5
Clinical Course and Management
- Diagnosis is primarily clinical 5
- Self-limiting condition typically resolving within two weeks
- Symptomatic treatment with antihistamines is usually effective 6
- No need for extensive laboratory evaluations or biopsies when clinical presentation is classic 1
Pitfalls and Caveats
- The striking appearance of lesions often causes parental anxiety and may lead to unnecessary hospitalizations and testing 2
- Distinguishing from erythema multiforme is critical as management approaches differ significantly
- Unlike urticarial vasculitis, individual lesions in urticaria multiforme resolve within 24 hours without residual changes 4
- The presence of fever does not exclude the diagnosis of urticaria multiforme 2
Diagnostic Approach
- Thorough history focusing on recent infections and medication use
- Careful examination of lesion morphology and duration
- Observation for associated angioedema and dermatographism
- In typical presentations, avoid unnecessary biopsies or extensive laboratory testing 1
Understanding the benign and self-limiting nature of urticaria multiforme is essential to avoid unnecessary interventions while providing appropriate symptomatic management with antihistamines.