Identifying Signs of Tinea Pedis: A Key to Understanding Clinical Variables
October 2015 | Volume 14 | Issue 10 | Supplement | s42 | Copyright © 2015
Theresa N. Canavan MD and Boni E. Elewski MD
Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL
Tinea pedis is a frequently encountered dermatophytosis affecting the superficial skin of the feet, primarily of adults. The prevalence of tinea pedis has increased over the last several decades due to an increase in multiple risk factors. Infection from dermatophytes is most common, but infection from other fungi can also result in tinea pedis. Four distinct clinical presentations occur: interdigital, moccasin,
vesicular, and acute ulcerative types. A variety of physical exam findings can help the clinician identify patients with tinea pedis.
J Drugs Dermatol. 2015;14(suppl 10):s42-s47.
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Superficial cutaneous fungal infections represent a diverse group of diseases caused by dermatophytes, yeasts (Candida albicans), and occasionally non-dermatophyte molds. The prevalence of superficial cutaneous fungal infections has increased over the past several decades and is seen in both immunocompetent and immunosuppressed patients around the world.
Dermatophytes are a group of closely related fungi that infect the skin, hair, and nails of both humans and animals. Tinea pedis, the most common dermatophytosis, is a superficial fungal infection of the plantar surface and frequently occurs in developed countries. Although tinea pedis is caused mostly by anthropophilic dermatophytes, zoophilic infections can occasionally occur and these are usually more inflammatory.
Over the past 30 years there has been an increase in the incidence of tinea pedis due to in part to growing urbanization and changes in recreational activities; and currently up to 25% of the population may be affected at any given time in the United States.1-4 Tinea pedis can provide a portal of entry for secondary bacterial infection, resulting in profound complications and morbidity.5
Only a few fungi are implicated in the vast majority of tinea pedis cases (Table 1). Trichophyton rubrum is by far the most common organism involved in tinea pedis, followed by specifies from within the T. mentagrophytes complex, Epidermophyton floccosum, and T. tonsurans.6 Although T. tonsurans is an uncommon cause of tinea pedis in adults, its prevalence is increasing.7 Of these fungi, only species from within the T. mentagrophytes complex have both anthropophilic and zoophilic varieties; T. rubrum, E. floccosum, and T. tonsurans are strictly anthrophophilic.8 In addition to being the most common cause of tinea pedis, T. rubrum is also responsible for approximately 90% of onychomycosis cases.9 Chronic untreated or undertreated tinea pedis is a predisposing risk factor for the development of onychomycosis.9 Patients who progress from tinea pedis to develop concurrent onychomycosis have infections that are far more challenging to eradicate.
The taxonomic classification for the T. mentagrophytes complex has undergone multiple revisions over time as our ability to differentiate species based on molecular studies and genetic information has improved. Within the T. mentagrophytes complex, T. interdigitale (previously called T. mentagrophytes var. interdigitale) is the most commonly isolated organism. It is almost strictly anthrophilic, but can be found rarely in animals. Also within the T. mentagrophytes complex is the T. mentagrophytes species, which is primarily zoophilic and is found in association with rodents (rats, hamsters, guinea pigs), rabbits, and ferrets. In humans, the T. mentagrophytes species can cause a highly inflammatory form of tinea pedis. Arthoderma benhamiae is a third species within the T. mentagrophytes complex; however, this species will not be discussed here as it is primarily zoophilic and only occasionally leads to tinea corporis and tinea capitis, but not tinea pedis. Finally, A. vanbreuseghemii is a mating type strain within the T. mentagrophytes complex and will also not be discussed.
In addition to the dermatophytes mentioned above, infections from non-dermatophyte molds can also result in tinea pedis. Outside of the Western hemisphere, non-dermatophyte molds are not uncommon isolates from foot infections. For example, an outpatient epidemiology study from Thailand reported that non-dermatophyte infections account for nearly 60% of cases of tinea pedis.10 Of these non-dermatophytes, Neoscytalidium dimidiatum and its hyaline mutant N. dimidiatum var. hyalinum (previously called S. lignicola) represent the overwhelmingly