Erythema multiforme is a common misdiagnosis in patients with urticaria multiforme.1,2 The erythema multiforme rash has a “target” lesion with outer erythema and central ecchymosis, which may develop blisters or necrosis. Lesions are fixed and last 2 to 3 weeks. Unlike urticaria multiforme, patients with erythema multiforme commonly have mucous membrane erosions and occasionally ulcerations. Facial and acral edema is rare. Treatment is largely symptomatic and can include glucocorticoids. Antiviral medications may be used to treat recurrences.1,2
Henoch-Schönlein purpura is an immunoglobulin A–mediated vasculitis that affects the skin, gastrointestinal tract, and joints.4,5 Patients often present with arthralgias, gastrointestinal symptoms such as abdominal pain and bleeding, and a nonpruritic, erythematous rash that progresses to palpable purpura in dependent areas of the body. Treatment is generally symptomatic, but steroids may be used in severe cases.4,5
Serum sickness-like reaction can manifest with angioedema and a similar urticarial rash (with central clearing) that lasts 1 to 6 weeks.1,2,6,7 However, patients tend to have a high-grade fever, arthralgias, myalgias, and lymphadenopathy while dermatographism is absent. Treatment includes discontinuing the offending agent and the use of H1 and H2 antihistamines and steroids, in severe cases.
Urticarial vasculitis manifests as plaques or wheals lasting 1 to 7 days that may cause burning and pain but not pruritis.2,5 Purpura or hypopigmentation may develop as the hives resolve. Angioedema and arthralgias are common, but dermatographism is not present. Triggers include infections, autoimmune disease, malignancy, and the use of certain medications. H1 and H2 blockers and nonsteroidal anti-inflammatory agents are first-line therapy.2
Step 1: Discontinue offending agents; Step 2: Recommend antihistamines
Treatment consists of discontinuing any offending agent (if suspected) and using systemic H1 or H2 antihistamines for symptom relief. Systemic steroids should only be given in refractory cases.
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