Onychomycosis of the Middle Finger of a Japanese Judo Athlete due to Trichophyton tonsurans.

We present a 17-year-old Japanese male high school student, who had applied steroid ointment for atopic dermatitis, with fingernail onychomycosis due to Trichophyton tonsurans. He was found positive for T. tonsurans infection based on hairbrush culture performed due to an epidemic of T. tonsurans infection in his judo club. The hairbrush culture method is very important in screening for this infection, and dermatologists should examine the entire body of athletes who are found positive using this method. For the diagnosis of T. tonsurans infection, other than the skin and hair, the nails should also be checked by dermoscopy because the fingernail may be the origin of this fungus.