A case of tinea nigra palmaris in Okinawa, Japan

We report a case of tinea nigra on the left palm of a 13-year-old girl. She had noticed a pigmented, asymptomatic macule on the left palm approximately 4-5 years prior to her first visit to our hospital. The color of the lesion tended to change before and after a bath; it became lighter after a bath and darkened some time later. Physical examination revealed that the macule was 4 cm x 5 cm in size, dark brown in color and irregularly shaped. Direct potassium hydroxide (KOH) microscopic examination from skin scrapings revealed branched brown hyphae with light brown septa. A fungal culture on Sabouraud's agar media produced wet, medium brown, yeast-like colonies, the surface of which later became black and shiny. A slide culture disclosed light brown, elliptic or peanut-shaped conidia comprised of one to two ampullaceous cells. Scanning electron microscopic examination of the conidia showed both annellation conidia with lunate bud scars and sympodial conidiogenesis. Using extracted DNA from separately cultured fungi, we performed polymerase chain reaction with the primers specific to Hortaea werneckii. The results showed positive bands. We performed direct sequencing with the DNA segments from the positive bands. The causative fungus in our case was determined to be type C of H. werneckii on the grounds of the base sequences obtained. The final diagnosis of the present case was made as tinea nigra by H. werneckii. We also report a brief survey of all the cases of tinea nigra reported in Japan to date.