Tinea pedis: causes, symptoms, diagnosis, and treatment

Tinea pedis, also known as athlete's foot, is the most common superficial mycosis, usually on the bilateral feet, soles, and intertriginous skin, manifested by vesicles, erosions, and scales, and can be divided into chronic hyperkeratotic, chronic intertriginous, acute ulcerative, and vesiculobullous tinea pedis according to the main clinical manifestations. Onychomycosis is often present concurrently.


Causes

The pathogens are dermatophytes, including trichophyton, microsporum, and epidermophyton, predominantly trichophyton. According to the current classification, the most common pathogens are trichophyton rubrum of trichophyton rubrum complex and trichophyton interdigitale of trichophyton mentagrophytes complex.

The high incidence of tinea pedis is associated with the anatomical characteristics of feet, including numerous sweat glands in the plantar area, excessive sweating, absence of sebaceous glands, and alkaline skin surface, which are conducive to fungal growth, and the thick stratum corneum provides rich nutrition for fungal growth. In addition, trichophyton rubrum and epidermophyton floccosum can form arthrospores in the scales, can survive for a long time in the natural environment, and are contagious, which increases the risk of foot infection.


Signs and Symptoms

Chronic hyperkeratotic tinea pedis is mainly manifested by hyperkeratosis, anhidrosis, absence of vesicles and pustules, and chapped skin in cold seasons, mostly on the heels and plantar skin, often symmetrically, and skin lesions can sometimes extend to the entire plantar skin and dorsal feet in severe cases.

Figure 1 chronic hyperkeratotic tinea pedis

Chronic intertriginous tinea pedis occurs frequently on the lateral 3 toes and is characterized by scales, erythema, and erosion.

Figure 2 chronic intertriginous tinea pedis

Acute ulcerative tinea pedis usually occurs in the interdigital skin between the 3rd and 4th toes and can spread to the dorsal feet or plantar area. Skin lesions are usually maceration and scales on the toe web. Common complications are secondary bacterial infections, cellulitis, and lymphangitis.

Figure 3 acute ulcerative tinea pedis

Vesiculobullous tinea pedis is usually on the plantar skin and is manifested by clustered or scattered vesicles, accompanied by pruritus. The vesicles are in deep skin, the wall of vesicles is not easy to be penetrated, and there are no red halos. The vesicles can dry and develop into crusts in few days. Skin lesions can extend peripherally, sometimes vesicles fuse into large blisters. The blister fluid is slightly yellowish white, and the blisters can progress into yellow pustules if secondary infections occur.

Figure 4 vesiculobullous tinea pedis


Histopathology

Intercellular edema, spongiosis, and cellular infiltration in the epidermis in the acute stage can be seen. The vesicles are located below the stratum corneum, and parakeratosis may be present. In the chronic phase, there are hyperkeratosis, acanthosis, and chronic inflammatory infiltration. Fungal hyphae can be occasionally found in the stratum corneum in periodic acid-schiff (PAS) stain.


Diagnosis

A diagnosis can be made based on clinical presentations. Potassium hydroxide (KOH) microscopic examination can assist in the diagnosis.


Treatment

Topical medications include imidazoles such as clotrimazole, econazole, miconazole, ketoconazole, bifonazole, isoconazole, sertaconazole, oxiconazole, and luliconazole, allylamines such as naftifine, terbinafine, and butenafine, other antifungal drugs such as amorolfine, ciclopirox, and liranaftate, and keratolytics such as salicylic acid.

Common systemic antifungals include terbinafine and itraconazol.