Unusual presentation of Microsporum canis in human hair

This study reports an unusual presentation of Microsporum canis in infected human hair in a three-year-old boy. Infected hairs showed ectothrix colonization with a mass of small conidia and numerous macroconidia typical of the genus Microsporum. The infected hairs also showed strong invasion by hyphae bearing small numbers of arthroconidia. These hyphae were thinner and longer than those normally found in hair and scalp. It is well known that in cases of tinea capitis due to M. canis, ectothrix arthroconidia formation is extrapilary and arises from intrapilary hyphae. In this case it seems that unusual quantities of hyphae were formed, and not all of them broke down into arthroconidia. They appeared to remain in the hair and to produce macroconidia, which were not formed outside the hair in contact with air, but instead seemed to remain in a deeper layer of the hair than the arthroconidia seen.