Other Tests
Mycologic features form the basis of tinea barbae diagnosis. [30] Procedures include direct microscopy, culture, and a Wood lamp examination showing fluorescence when Microsporum canis infection causes tinea barbae. Molecular identification is another option. [31]
Specimen selection and collection is important. Usually, the material consists of infected hairs (depilated with forceps) and pustular masses. In the superficial variety, which resembles tinea corporis, collect scrapings from the border of the lesion where the inflammatory reaction is more severe. Taking material from the lesion's border increases the possibility of detecting fungi on direct microscopy and culture. Send the specimen for culture, or examine it for fungus.
Direct microscopic examination is performed rapidly and easily; however, it requires experience. Place the material on a slide and add a solution of 10-20% potassium hydroxide, with or without dimethyl sulfoxide. This solution provides visualization of fungal elements. Gently warm the slide, especially if no dimethyl sulfoxide is added. Some recommend using special stains, such as chlorazol black E stain or Parker blue-black ink. Direct microscopy usually shows hyphae and/or arthroconidia. Wait for some minutes before evaluating the preparation under microscopy, or reexamine the slide after one-half hour, since fungal elements may be difficult to see just after addition of potassium hydroxide solution.
Culture identifies the causative fungus and usually is performed on Sabouraud agar with the addition of cycloheximide and chloramphenicol. These two substances inhibit bacterial and other fungal growth to obtain pure dermatophyte colonies. Cultures take approximately 3 weeks to become positive, and final fungal identification is based primarily on morphology and microscopy of the colonies. Occasionally, additional tests are required. Special media for rapid dermatophyte identification that include a color indicator currently are available. In the presence of dermatophytes, the color changes from yellow to bright red.
Histologic Findings
Biopsy specimens occasionally may be required to diagnose tinea barbae. Biopsy shows folliculitis and perifolliculitis with a mixed cellular infiltrate and spongiotic alterations within the follicular epithelium. Lymphocytes or neutrophils also may be evident within follicular epithelium. Neutrophils also may be seen within follicular keratin as microabscesses.
Since fungal elements often are difficult to visualize with hematoxylin and eosin stain, periodic acid-Schiff stain is recommended. Arthroconidia and/or hyphae may be evident within the hair shaft and in the hair follicle. An inflammatory infiltrate is present in the dermis, which in chronic lesions may contain giant cells.
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Inflammatory tinea barbae resulting from Trichophyton mentagrophytesvar granulosuminfection.
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Wax model of kerionlike tinea barbae. Courtesy of the Museum of the Department of Dermatology, University of Medicine, Wroclaw, Poland.
