"Urticaria multiforme": a case series and review of acute annular urticarial hypersensitivity syndromes in children.

Acute annular urticaria is a common and benign cutaneous hypersensitivity reaction seen in children that manifests with characteristic annular, arcuate, and polycyclic urticarial lesions in association with acral edema. It is mistaken most often for erythema multiforme and, occasionally, for a serum-sickness-like reaction. Although these 3 entities may present in a similar manner, specific clinical features help to distinguish them, and it is important for the clinician to be able to differentiate among them. We present herein a series of 18 patients who were given a diagnosis of acute annular urticaria and review the clinical distinctions between acute annular urticaria, serum-sickness-like reactions, and erythema multiforme. Because of the frequency of its clinical confusion with erythema multiforme, we propose the term "urticaria multiforme" as a more apt description to highlight the distinctive clinical features of this urticaria variant.