Introduction: The ability to diagnose and differentiate life-threatening from benign rashes is a necessity for care providers working with children. We present two cases of urticaria multiforme (UM), a benign hypersensitivity rash commonly mistaken for more severe diseases such as erythema multiforme (EM) and conditions associated with purpuric lesions. UM has a remarkably different course and severity.
Case 1: A 12-month-old previously healthy girl presented to clinic for a rash characterized by palpable pink wheels that progressed from her chest and thighs to the remainder of her extremities. The rash spared her palms, soles and mucus membranes. The child appeared well, but had been diagnosed with bilateral otitis media eight days previously and treated with amoxicillin. She also received Varicella and Mumps/Measles/Rubella vaccines the week prior and visited Ireland three weeks prior. Amoxicillin was discontinued. On day two, she returned to clinic because the rash had become intensely pruritic, the palpable pink wheels had developed central duskiness that looked similar to bruising, and her hands, feet and face were edematous. There were no target lesions. Apart from her apparent pruritis, she continued to appear well and was sent home with diphenhydramine with resolution over the next 3 days.
Case 2: A 12-month-old boy presented to the emergency department (ED) for sudden onset of palpable pink wheels on his face and torso with facial erythema. His rash did not appear painful or pruritic, and his exam was otherwise remarkable only for two crusted circular lesions on his bottom lip that developed the day prior. The child was diagnosed with acute otitis media one week previously and was taking amoxicillin. The amoxicillin was discontinued. The patient returned to the ED the following morning with intense pruritus, progression of his rash to involve all extremities, significant edema of his hands, feet and face and, most notably, a dusky hue evolving over his abdomen and his lower extremities. Patient was hospitalized and treated with diphenhydramine and cetirizine. He was discharged after four days with significant improvement.
Discussion: UM is a common rash that can have multiple triggers, including viral infections, vaccines, and medications, and is frequently mistaken for other diagnoses. Both of our cases can easily be distinguished from EM because the rashes lacked mucous membrane involvement, target lesions, and spared palms and soles. Though sometimes the dusky appearance may be mistaken for EM target lesions, in UM there is no central target lesion. Both of our cases were either hospitalized or referred to subspecialty care because of concern for purpura and potential for severe disease. Conditions associated with purpuric lesions, such as meningococcemia and systemic vasculitis are usually associated with ill-appearance and sepsis or other systemic symptoms. A search of PubMed and Cochrane databases using the terms “urticaria” and “urticaria multiforme” revealed only a single case series about UM. These cases of UM provide additional information on this common rash enabling providers to recognize this condition, differentiate it from other more serious diseases, ease parental anxiety and avoid unnecessary hospitalizations and repeat visits. Dr. Kimberly Wenner and Dr. LoRanee Braun also contributed to this case series.
