Lab work was ordered and came back within normal range, except for an elevated white blood cell count (19,700/mm3; reference range, 4500-13,500/mm3). His mild systemic symptoms, skin lesions without blistering or necrosis, acral edema, and the absence of lymphadenopathy pointed to a diagnosis of urticaria multiforme.
Urticaria multiforme, also called acute annular urticaria or acute urticarial hypersensitivity syndrome, is a histamine-mediated hypersensitivity reaction characterized by transient annular, polycyclic, urticarial lesions with central ecchymosis. It typically manifests in children ages 4 months to 4 years and begins with small erythematous macules, papules, and plaques that progress to large blanchable wheals with dusky blue centers.1-3 Lesions are usually located on the face, trunk, and extremities and are often pruritic (60%-94%).1-3 The rash generally lasts 2 to 12 days.1,3
Patients often report a preceding viral illness, otitis media, recent use of antibiotics, or recent immunizations. Patients also often have associated facial or acral edema (72%).1 Children with significant edema of the feet may find walking difficult, which should not be confused with arthritis or arthralgias.
The diagnosis is made clinically and should not require a skin biopsy or extensive laboratory testing. When performed, laboratory studies—including CBC, erythrocyte sedimentation rate, C-reactive protein, and urinalysis—are routinely normal. The differential diagnosis in this case included erythema multiforme, Henoch-Schönlein purpura, serum sickness-like reaction, and urticarial vasculitis.1,2,4
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.
Our patient’s amoxicillin was discontinued, and he was started on a 14-day course of cetirizine 5 mg bid and hydroxyzine 10 mg at bedtime. He was also started on triamcinolone 0.1% cream to be applied twice daily for 1 week. During his 3-day hospital stay, his fever resolved, and his rash and edema improved.
During an outpatient follow-up visit with a pediatric dermatologist 2 weeks after discharge, the patient’s rash was still present and dermatographism was noted. In light of this, his parents were instructed to continue giving the cetirizine and hydroxyzine once daily for an additional 2 weeks and to return as needed.
This case was adapted from: Cook JS, Angles A, Morley E. Urticaria and edema in a 2-year-old boy. J Fam Pract. 2021;70:353-355.
Photos courtesy of Jeffrey S. Cook, MD, FAAFP