Mycological Considerations in the Topical Treatment of Superficial Fungal Infections
February 2016 | Volume 15 | Issue 2 | Supplement Individual Articles | 49 | Copyright © February 2016
Ted Rosen MD
Baylor College of Medicine, Houston, TX
Trichophyton rubrum remains the most common pathogenic dermatophyte in the United States, Europe, and industrialized Asia, although other species are predminant elsewhere. Candida albicans is the most common pathogenic yeast, with other species occasionally encountered. Just a few of the 14 described species of Malassezia cause pityriasis versicolor worldwide. FDA approval does not always accurately reflect the potential utility of any given topical antifungal agent. Azole, hydroxypyridone, and allylamine agents are beneficial in the management of dermatophytosis; however, the allylamines may lead to faster symptom resolution and a higher degree of sustained response. Although in actual clinical use the allylamines have all shown some activity against superficial cutaneous candidiasis and pityriasis versicolor, the azole agents remain drugs of choice. Ciclopirox is an excellent broad-spectrum antifungal agent. Optimal topical therapy for superficial fungal infections cannot yet be reliably based upon in-vitro laboratory determination of sensitivity. Inherent antibacterial and anti-inflammatory properties possessed by some antifungal agents may be exploited for clinical purposes. Candida species may be azole-insensitive due to efflux pumps or an altered target enzyme. So-called “antifungal resistance” of dermatophyets is actually due to poor patient adherence (either in dosing or treatment duration), or to reinfection. J Drugs Dermatol
. 2016;15(Suppl 2):s49-55.
Superficial fungal infections – those affecting the skin, hair and nails – are extraordinarily common worldwide. About 20% to 25% of the world’s population will be affected by at least one superficial fungal infection during their lifetime.1 Superficial mycoses are caused by Candida species, the yeast forms responsible for pityriasis versicolor, select nondermatophyte molds, and dermatophytes, with the latter being the most prevalent globally.2,3 The justifications for treatment of superficial mycoses include: cosmetic distress, presence of pruritus or pain, potential for spread from one body site to another, possible transmission to unaffected individuals, and prevention of secondary bacterial superinfection or persistent nail dystrophy.4-7 When measured, successful therapy of superficial mycoses is associated with an improved quality of life.8-10
For a variety of reasons detailed elsewhere,11 it is likely that both the incidence and prevalence of superficial fungal infections will increase. Thus, health care practitioners (HCPs) remain in search of simple, safe, convenient, and effective therapeutic interventions. This manuscript reviews mycologic aspects of this subject, with a goal of offering concrete and clinically relevant suggestions. This review will not address superficial mycoses, which typically require oral therapy (such as tinea capitis).
Epidemiology of Superficial Mycoses
It is difficult to reliably determine both the overall incidence and prevalence of the various superficial mycoses worldwide because epidemiologic studies performed in one city/locale may not be representative of the overall disease pattern of that country; similarly, findings in one country may not be representative of the overall disease pattern of that region/continent. Finally, fungal disease patterns differ greatly from continent to continent.1,2 Moreover, the predominant pathogenic fungal species is somewhat dependent on which type of superficial mycosis is most common, tinea pedis or tinea capitis. Finally, the local pattern of highly prevalent dermatophyte organisms may be influenced or modified by such factors as: changes in socioeconomic conditions, alterations in typical lifestyle, recent migration, and expansion of tourism.1 With the foregoing cautionary caveats in mind, some generalizations can be made1,2,12-14:
Some species are worldwide T. rubrum, T. mentagrophytes var. interdigitale (now simply called T. interdigitale), M. canis, and E. floccosum.
Other species are characteristically restricted to select geographic regions; examples include: T. schoenleinii (Eurasia, Africa), T. soudanense (Africa), T. violaceum (Africa, Asia, and Europe), and T. concentricum (Pacific Islands, Far East, and India). Patients presenting with dermatophytosis who are visiting or emigrating from these areas may well harbor an organism common in their native land. Cultural identification of the offending pathogen is advisable in order to properly direct treatment.
The vast majority of cases of onychomycosis, tinea cruris, tinea corporis, and tinea pedis are currently caused by T. rubrum, the