Laboratory Studies
Direct microscopic examination may be performed. Skin scrapings, nail specimens, or plucked hairs are treated with potassium hydroxide and examined. Hyphae can be visualized in skin and nails. Spores within or around the hair shaft can be detected.
Fungal cultures can be performed for precise identification of the species.
Wood light (UV light) examination may be performed. This examination is used mainly for the diagnosis of tinea capitis. Hairs infected with M audouinii and M canis produce a brilliant yellow-green fluorescence. T schoenleinii causes a dull green fluorescence.
Histology is not needed, but biopsy findings would show spongiosis, parakeratosis (that may alter with orthokeratosis), and a superficial inflammatory infiltrate. Neutrophils may be seen in the stratum corneum, which is a significant diagnostic clue. On occasion, septate branching hyphae are seen in the stratum corneum. Special fungal stains (eg, periodic acid-Schiff, Gomori methenamine silver) may be required.
Procedures
A biopsy may be needed in recalcitrant or atypical disease.
As mentioned above, dermatophyte infection occasionally leads to formation of a kerion, which is a boggy, large, inflammatory scalp mass caused by a severe inflammatory reaction to the dermatophyte. A kerion may result in scarring hair loss. A kerion may also have pustules and crusting and is commonly mistaken for an abscess. It is important to recognize a kerion because incision and drainage is not indicated. Therefore, other than a biopsy or culture that may be taken by an experienced dermatologist, no procedure is commonly performed by the emergency department physician. [7]
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Wax model of kerionlike tinea barbae. Courtesy of the Museum of the Department of Dermatology, University of Medicine, Wroclaw, Poland.
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Tinea capitis; gray patch ringworm. Gray patch refers to the scaling with lack of inflammation, as noted in this patient. Hairs in the involved areas assume a characteristic dull, grayish, discolored appearance and are broken and shorter.
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Typical lesions of kerion celsi on the vertex scalp of a young Chinese boy. Note numerous bright yellow purulent areas on skin surface, surrounded by adjacent edematous, erythematous, alopecic areas. Culture from the lesion grew Trichophyton mentagrophytes. Courtesy of Skin Diseases in Chinese by Yau-Chin Lu, MD. Permission granted by Medicine Today Publishing Co, Taipei, Taiwan, 1981.
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Annular plaque (tinea corporis).
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Tinea favosa of the scalp shows erythematous lesions with pityroid scaling. Some hairs are short and brittle.
Tables
Species |
Natural habitat |
Incidence |
E floccosum |
Humans |
Common |
T rubrum |
Humans |
Very common |
T interdigitale |
Humans |
Very common |
T tonsurans |
Humans |
Common |
Trichophyton violaceum |
Humans |
Less common |
Trichophyton concentricum |
Humans |
Rare |
Trichophyton schoenleinii |
Humans |
Rare |
Trichophyton soudanense |
Humans |
Rare |
Microsporum audouinii |
Humans |
Less common |
Microsporum ferrugineum |
Humans |
Less common |
T mentagrophytes |
Mice, rodents |
Common |
Trichophyton equinum |
Horses |
Rare |
Trichophyton erinacei |
Hedgehogs |
Rare |
Trichophyton verrucosum |
Cattle |
Rare |
M canis |
Cats |
Common |
Microsporum gypseum |
Soil |
Common |
Microsporum nanum |
Soil/pigs |
Rare |
Microsporum cookei |
Soil |
Rare |
