Fontana-positive grains in mycetoma caused by Microsporum canis.

We describe mycetoma caused by Microsporum canis occurring in a 9-year-old African-American girl. Pathologic evaluation showed a granulomatous dermatitis with numerous large fungal grains containing septate hyphae that were Fontana-Masson positive. Two cultures of pure grains grew M. canis. Mycetoma due to dermatophytes is very uncommon. The few instances reported have been pseudomycetoma (grains in the absence of sinus tracts). Our patient developed sinus tracts (true mycetoma). No prior reports were found of M. canis staining Fontana positive. Differentiation of dermatophyte-induced mycetoma from kerion is important because mycetomas require a combined approach including surgical debridement in addition to oral antifungal therapy.