Overview
Definition
Transient, pruritic, edematous papules and plaques (wheals) caused by mast cell degranulation.
Epidemiology
Lifetime prevalence of ~20%.
Etiology & Risk Factors
- Acute (<6 weeks): Infections, foods, medications (Penicillin, NSAIDs), insect stings
- Chronic (>6 weeks): Autoimmune (anti-IgE or anti-FcεRI autoantibodies), idiopathic
Clinical Symptoms
- Intensely itchy wheals with surrounding erythema
- Lesions blanch with pressure
- Individual lesions appear and resolve within 24 hours
- May be accompanied by angioedema
Clinical Approach
Diagnosis
- Clinical diagnosis
- Allergy testing (rarely helpful for chronic idiopathic cases)
Management
- Second-generation H1 antihistamines (Cetirizine, Loratadine)
- Increase dose up to 4x standard
- Omalizumab (anti-IgE) for refractory chronic cases
- Epinephrine (if anaphylaxis)
Complications
- Anaphylaxis (if acute allergic trigger)
- Angioedema (airway compromise)
- Sleep disruption due to pruritus