Tinea nigra

Tinea nigra (also known as "superficial phaeohyphomycosis,"^[1] and "Tinea nigra palmaris et plantaris"^[1]) is a superficial fungal infection that causes dark brown to black painless patches on the palms of the hands and the soles of the feet.

Tinea nigra affects the outermost layer of skin, called the stratum corneum. Tinea nigra causes a black or brown patch on the skin. Although a patch of tinea nigra may be mistaken for the more serious skin discolorations of melanoma, tinea nigra is actually a very benign condition that often causes no symptoms apart from its appearance.

The period of incubation of tinea nigra varies from two to seven weeks. It typically presents as unilateral, asymptomatic sharply demarcated of one or more brown or black macules, wich can join and envolve centrifugally growing to between one and five centimeters. There is minimum desquamation and well delimited borders localize mainly on the palmar regions and the fingers, but rarely on the plants of the feet, dorsal aspects of the hands, cervical and back region [4]. Potassium hydroxide preparation of lesional skin scrapings of the lesion show numerous pigmented septate hyphae. Cultures on Sabouraud agar at room temperature show slow-growing, moist and shiny black colonies [5]. They are composed of oval to spindle-shaped cells, many of them with a central cross wall. These lesions are quite characteristic. However, they can be misdiagnosed as a malignant melanoma or a junctional melanocytic nevus and unnecessary biopsies may performed [6]. Thus, dermoscopy is a fast, useful, clinical adjunctive tool in differentiating tinea nigra from melanocytic lesion [7, 8]. Gupta et al. [9] originally described the dermatoscopic findings of tinea nigra as a nonmelanocytic pattern of pigmented spicules, thus aiding in differentiating this lesion from a pigmented lesion that should be biopsied. Treatment could be performed with topical antifungal therapy, although keratolytic agents have also been used [6]. Complete resolution typically occurs with two weeks of treatment. There is a report of successful treatment with oral itraconazole [9]. There is rarely any recurrence

Causes

This infection is caused by the fungus formerly classified as Exophiala werneckii but more recently classified as Hortaea werneckii.^[3]

The causative organism has also been described as Phaeoannellomyces werneckii.^[4]

[edit]Diagnosis

Diagnosis of tinea nigra causing fungus is made on microscopic examination of skin scrapings, mixed with potassium hydroxide (KOH).^[5] The KOH lyses the nonfungal debris.^[5]

Potassium hydroxide preparation of lesional skin scrapings demonstrated numerous pigmented septate hyphae, with varying diameter (Fig. 5). The child was treated with 1 percent Isoconazole cream twice a day for 3 weeks with complete resolution.

After 21 days the culture on Sabouraud agar at room temperature showed moist black colonies, which were identified asPhaeoannelomyces werneckii

[edit]Treatment

Treatment consists of topical application of dandruff shampoo, which contains selenium sulfide, over the skin. Topical antifungal imidazoles may also be used, such as Ketoconazole. This is the same treatment plan for tinea or pityriasis versicolor.