A girl with circular erythema on the forearm

An 11 year old girl was referred to the dermatology clinic with circular urticarial lesions mainly on the forearm of the non-dominant arm (fig1, left panel). The lesions appeared every morning and lasted for 2-3 hours accompanied by pain. During hospital admission two weeks previously, the patient had been told the lesions were due to vasculitis. She received a course of systemic glucocorticoid treatment (40 mg/day methylprednisolone intravenous injection for 12 days), but the lesions did not improve. Routine tests for complete blood count, blood glucose, liver and renal function tests, antineutrophil cytoplasmic antibody, and serum complement were within normal range. Histological examination of a skin biopsy sample showed a non-specific pattern. On physical …