Tinea Capitis Workup

Updated: Feb 21, 2020
  • Author: Marc Zachary Handler, MD; Chief Editor: Dirk M Elston, MD  more...
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Laboratory Studies


Laboratory diagnosis of tinea capitis depends on examination and culture of skin rubbings, skin scrapings, or hair pluckings (epilated hair) from lesions.

Before specimen collection, any ointment or other local applications present should be removed with alcohol.

Infected hairs appearing as broken stubs are best for examination. They can be removed with forceps without undue trauma or collected by gentle rubbing with a moist gauze pad; broken, infected hairs adhere to the gauze. A toothbrush may be used in a similar fashion. [19] Alternatively, affected areas can be scraped with the end of a glass slide or with a blunt scalpel to harvest affected hairs, broken-off hair stubs, and scalp scale. This is preferable to plucking, which may remove uninvolved hairs. Scrapings may be transported in a folded square of paper. Skin specimens may be scraped directly onto special black cards, which make it easier to see how much material has been collected and provide ideal conditions for transportation to the laboratory; however, affected hairs are easier to see on white paper than on black paper. Alternatively, a swab-culture technique has been proposed where a moistened cotton tip applicator from a bacterial culture swab is used to gather a sample and sent to the laboratory for culture growth. [20]

Definitive diagnosis depends on an adequate amount of clinical material submitted for examination by direct microscopy and culture. The turn-around time for culture may take several weeks.

Selected hair samples are cultured or allowed to soften in 10-20% potassium hydroxide (KOH) before examination under the microscope. Examination of KOH preparations (KOH mount) usually determines the proper diagnosis if a tinea infection exists.

Conventional sampling of a kerion can be difficult. Negative results are not uncommon in these cases. The diagnosis and decision to treat lesions of kerion may need to be made clinically. A moistened standard bacteriological swab taken from the pustular areas and inoculated onto the culture plate may yield a positive result. [21]

Microscopic examination of the infected hairs may provide immediate confirmation of the diagnosis of ringworm and establishes whether the fungus is small-spore or large-spore ectothrix or endothrix.

Culture provides precise identification of the species for epidemiologic purposes. [22] Primary isolation is carried out at room temperature, usually on Sabouraud agar containing antibiotics (penicillin/streptomycin or chloramphenicol) and cycloheximide (Acti-Dione), which is an antifungal agent that suppresses the growth of environmental contaminant fungi. In cases of tender kerion, the agar plate can be inoculated directly by pressing it gently against the lesion. Most dermatophytes can be identified within 2 weeks, although T verrucosum grows best at 37°C and may have formed only into small and granular colonies at this stage. Identification depends on gross colony and microscopic morphology. Specimens should be inoculated on to primary isolation media, such as Sabouraud dextrose, and incubated at 26-28°C for 4 weeks. The growth of any dermatophyte is significant.

In some cases, other tests involving nutritional requirements and hair penetration in vitro are necessary to confirm the identification.

Wood lamp examination

In 1925, Margarot and Deveze observed that infected hairs and some fungus cultures fluoresce in ultraviolet light. The black light commonly is termed Wood lamp. Light is filtered through a Wood nickel oxide glass (barium silicate with nickel oxide), which allows only the long ultraviolet rays to pass (peak at 365 nm). Wood lamp examination is useful for certain ectothrix infections (eg, those caused by M canis,M audouinii,Microsporum rivalieri). In cases with endothrix infection, such as T tonsurans, however, negative Wood lamp examination findings are of no practical value for screening or monitoring infections. [23]

Hairs infected by M canis, M audouinii, M rivalieri, and M ferrugineum fluoresce a bright green to yellow-green color (see the image below).

Wood lamp examination of a gray-patch area on the Wood lamp examination of a gray-patch area on the scalp. In Microsporum canis infection, scalp hairs emit a diagnostic brilliant green fluorescence. Trichophyton tonsurans does not fluoresce with Wood lamp.

Hairs infected by T schoenleinii may show a dull green or blue-white color, and hyphae regress leaving spaces within the hair shaft. T verrucosum exhibits a green fluorescence in cow hairs, but infected human hairs do not fluoresce. The fluorescent substance appears to be produced by the fungus only in actively growing infected hairs. Infected hairs remain fluorescent for many years after the arthroconidia have died.

When a diagnosis of ringworm is under consideration, the scalp is examined under a Wood lamp. If fluorescent infected hairs are present, hairs are removed for light microscopic examination and culture. Infections caused by Microsporum species fluoresce a typical green color.

Unfortunately, most tinea capitis infections in North America are caused by T tonsurans and do not demonstrate fluorescence. [24]

In favus, infected hairs appear yellow (see the image below).

Wood lamp examination of a gray-patch area on the Wood lamp examination of a gray-patch area on the scalp. In Microsporum canis infection, scalp hairs emit a diagnostic brilliant green fluorescence. Trichophyton tonsurans does not fluoresce with Wood lamp.


Serology  is not required for a diagnosis of dermatophytosis.

Dermoscopy and videodermatoscopy

Dermoscopy has been proposed as a way to make a diagnosis of tinea capitis, and even differentiate tinea capitis organisms. [25] T tonsurans has been described as having multiple comma-shaped hairs and M canis with dystrophic and elbow-shaped hairs. [26]

A small study in patients with tinea capitis from M canis found that comma hairs were a prominent and distinctive feature on videodermatoscopy; comma hairs were not seen in patients with alopecia areata. [27]


Histologic Findings

Skin biopsy with particular emphasis on examination of infected hairs with special histochemical stains aids in the identification of the causative fungus, especially in cases of fungal folliculitis (Majocchi granuloma) and onychomycosis. Bullous tinea demonstrates subepidermal edema and reticular degeneration of the epidermis. Tinea corporis demonstrates subacute and chronic dermatitis with or without follicular inflammation and destruction. Suppurative folliculitis may be present. In the mildest form, hyperkeratosis, parakeratosis, spongiosis, slight vasodilatation, and a perivascular inflammatory infiltrate in the upper dermis are present. Fungal hyphae can be demonstrated using routine hematoxylin and eosin stain, and identification can be facilitated by using special stains. Periodic acid-Schiff stain with diastase digestion or counterstained with green dye facilitates identification of fungal elements. See the image below.

Photomicrograph depicting an endoectothrix invasio Photomicrograph depicting an endoectothrix invasion of a hair shaft by Microsporum audouinii. Intrapilary hyphae and spores around the hair shaft are seen (hematoxylin and eosin stain with Periodic acid-Schiff counterstain, magnification X 250).

Fungi are seen sparsely in the stratum corneum (see the first image below). Hyphae extend down the hair follicle, growing on the surface of the hair shaft. Hyphae then invade the hair, penetrate the outermost layer of hair (ie, cuticle), and proliferate downward in the subcuticular portion of the cortex, gradually penetrating deep into the hair cortex. Pronounced inflammatory tissue reaction with follicular pustule formation surrounding hair follicles is seen in patients with the clinical form of infection termed kerion celsi (see the second image below).

Fungal hyphae and yeast cells of Trichophyton rubr Fungal hyphae and yeast cells of Trichophyton rubrum seen on the stratum corneum of tinea capitis. Periodic acid-Schiff stain, magnification 250X.
Pronounced inflammatory tissue reaction with folli Pronounced inflammatory tissue reaction with follicular pustule formation surrounding a hair follicle seen in a patient with clinical form of infection, termed kerion celsi. No fungal hyphae or spores were identified in the lesion in either tissue sections or culture. Fluorescein-labeled Trichophyton mentagrophytes antiserum cross-reacted with antigens of dermatophyte in the infected hairs within the pustule (hematoxylin and eosin stain, magnification X 75).

In endothrix infection, spherical–to–box-like spores are found within the hair shaft. This type of infection is caused by T tonsurans or T violaceum.

In ectothrix infection, organisms form a sheath around the hair shaft. In contrast to endothrix infection, destruction of the cuticle by hyphae and spores occurs.