(BMJ)—A 4-year-old boy presented with an itchy red lesion on his upper thigh that had been present for 4 days. He had no preceding injury or insect bites. The household had no pets, and no other family members were affected. Exam: annular, scaling, erythematous 1.5x1.5-cm lesion on upper thigh. What’s the dx?
Do-it-yourself tattoo
Nummular eczema
Granuloma annulare
Tinea corporis
Erythema annulare centrifugum
You are correct. Direct microscopic exam of the lesion showed fungal hyphae, and cx confirmed Microsporum canis. M. canis infections that cause tinea corporis are commonly associated with dog or cat exposure. Further questioning revealed that the child had been in indirect contact with stray cats in his neighborhood. The lesion that was unusually shaped like a smiling face was thought to be secondary to scratching, which can result in atypical appearances of tinea corporis lesions. A careful hx is needed to establish the dx.

BMJ 2021;374:n1964
By vgreene, 14 October, 2021

APS