(BMJ)—A 4-year-old boy presented with an annular erythema on his nose that had begun as a small itchy macule 7 days earlier. The lesion expanded after tx with topical steroids for presumed discoid eczema. He had no hx of insect bites or injury. The household had a cat. Exam: 1x1-cm annular red lesion without scaling on nose. What’s the dx?
Herpes simplex
Granuloma annulare
Tinea faciei incognito
Rosacea
Perioral dermatitis
You are correct. Tinea faciei incognito is a superficial dermatophytosis that occurs on the glabrous skin of the face. Typically, lesions are singular or multiple annular scaling patches with central clearing. Steroid tx can mask the typical features of tinea, a phenomenon known as tinea incognito. Skin scraping revealed numerous fungal hyphae and fungal cx grew Microsporum canis, one of the most common causes of tinea faciei. Most M. canis infections are associated with exposure to sick or subclinically infected animals.

The boy was treated with topical terbinafine for 4 weeks with complete remission and no recurrence at 2-month follow-up. His cat was diagnosed with dermatophytosis and was also treated with topical terbinafine.

BMJ 2021;374:n1952