Superficial Dermatophyte Infections of the Skin

Disease Burden

Dermatophyte infections are among the most common dermatologic conditions and are frequently refractory to treatment, leading to recurrence. In 2010, fungal skin diseases were the fourth most common of all diseases worldwide. The prevalence varies across the age spectrum; men are more likely to be affected than women. With the exception of tinea capitis, which primarily affects prepubertal children, the vast majority of dermatophytoses occur in adult hosts. Although dermatophytes rarely undergo deep local invasion and systemic dissemination, they can cause considerable morbidity, particularly in immunocompromised hosts.

Pathogenesis and Risk Factors

Dermatophytes are not endogenous pathogens. Transmission can occur directly from person to person (anthropophilic organisms), animal to person (zoophilic organisms), and soil to person (geophilic organisms) as well as from fomites like hair brushes and hats. Infective spores in dermal scales and hair can remain viable for months to years. Once the infectious elements of the fungus (arthroconidia) enter the skin, they germinate and invade the superficial skin layers. Dermatophytosis may cause defects in the skin barrier, which serve as a portal of entry to bacterial infections such as cellulitis. Disease severity is affected by several factors: sebum (which has an inhibitory effect on dermatophytes), the cutaneous barrier, genetic susceptibility to certain fungal infections, and the host’s immune system.

Clinical Features

Tinea Capitis

Tinea capitis is an infection of the scalp and hair shafts. It is most common in children and more common in boys than girls. Poor hygiene and overcrowding can foster transmission, which can occur through inanimate objects such as hats, brushes, and pillowcases. In the United States, 90% to 95% of tinea scalp infection is caused by the anthropophilic dermatophyte Trichophyton tonsurans , which does not fluoresce. Before 1950, fluorescent Microsporum species were the most common cause. KOH, fungal culture, and Wood lamp examination can be used for diagnostic testing. Tinea capitis begins with a small papule, which spreads to form scaly, irregular, or well-demarcated areas of alopecia. “Black dot” alopecia is produced when swollen hairs fracture a few millimeters from the scalp. Cervical and occipital lymphadenopathy may be prominent. A boggy, sterile inflammatory mass known as a kerion may also be seen, which can result in permanent alopecia if not treated promptly.

There are many scalp and hair conditions that lead to scaling or alopecia (scarring and nonscarring) that are not caused by fungal infections. When scaling and inflammation are prominent, diagnoses to be ruled out include atopic dermatitis, seborrheic dermatitis, and psoriasis. When alopecia is prominent, other diagnoses to consider include alopecia areata, traction alopecia, and trichotillomania.

Systemic antifungal therapy is required to penetrate the hair follicles. Griseofulvin 20 to 25 mg/kg/day for 8 weeks is commonly recommended ( Fig. 22.1 ). Several other agents—including itraconazole, terbinafine, and fluconazole—have been reported as effective and safe. They allow a shorter course of treatment and can be used in patients with griseofulvin allergy or in recalcitrant cases. Terbinafine may be more effective in cases due to T. tonsurans, whereas griseofulvin is likely more effective in cases due to M. canis. Preventive measures are also important, because the disease is contagious; all individuals residing with the infected patient should be evaluated and appropriately treated. Adjunctive topical therapy with antifungal shampoo, such as 2% ketoconazole or 2.5% selenium sulfide, may be useful to decrease shedding of viable fungi and spores.

Clinical Vignette

A 52-year-old man presented with an itchy rash on his left wrist, which had been present for 3 months. He had treated it with over-the-counter hydrocortisone with minimal improvement, and the lesions appeared to be spreading. His skin exam was notable for a 5-cm area of affected skin containing erythematous scaly papules with admixed pustules. KOH examination of the affected area reveals fungal hyphae. A diagnosis of Majocchi granuloma, a superficially invasive dermatophyte infection usually caused by T. rubrum , was made. Patients with Majocchi granuloma often have a history of corticosteroid use, minor trauma, immunosuppression, and/or of onychomycosis or tinea corporis. A KOH examination is not always positive; if it is negative, a skin biopsy with fungal staining may be required to make the diagnosis. Systemic antifungal treatment is necessary. Example regimens include terbinafine 250 mg PO daily for 4 weeks.