most common dermatophyte in both industrialized countries and in urban settings of emerging nations; In North America, as well as in most of Europe and Asia, the second most commonly encountered dermatophyte is T. interdigitale.
By contrast, in Southern Europe, Arabic countries, and rural locations in the Americas, zoophilic dermatophytes, such as M. canis or T. verrucosum, may be common pathogens.
When dealing with dermatophytes, the HCP must always take into account specific, individualized circumstances. For example, a patient who is involved with breeding, caring for, or riding horses might develop a dermatophytosis due to T. equinum, an otherwise unusual isolate.
Improvements in sanitation and socio-economic status may accompany urbanization, and the latter is generally associated with a decline in zoophilic and geophilic dermatophyte and a concurrent increase in anthropophilic dermatophyte infections.
Dermatophytes traditionally and primarily associated with tinea capitis can cause tinea corporis and even tines pedis (eg, M. canis, T. tonsurans).
Clinical infections, which unequivocally suggest dermatophytosis, may, in fact, be due to non-dermatophyte molds. Examples include: Neoscytalidium dimidiatum and N. hyalinum-induced tines pedis and as well as onychomycosis due to Acremonium, Aspergillus species, Fusarium species, Scopulariopsis brevicaulis, and other opportunistic molds. Such infections are highly treatment resistant, and failure of routine therapy should prompt mycological investigation for such rare organisms.
Although Malassezia species were discovered over a century and a half ago, their fastidious nature coupled with difficult culture and speciation techniques, have restricted research. New molecular techniques have facilitated understanding these lipophilic, non-keratolytic fungi. There are now 14 species within the genus Malassezia; M. globosa, M. furfur, M. restrica, and M. sympodialis are the common etiologic organisms associated with pityriasis versicolor.15 The prevalence of pityriasis versicolor varies from negligible to up to 50% of populations in tropical and subtropical environments.16 It is also more common among physically active, young individuals.17 Under the correct conditions, the fungi responsible for pityriasis versicolor can cause: catheter-associated fungal sepsis, peritoneal dialysis-associated peritonitis, mastitis, sinusitis, malignant otitis, and septic arthritis.15
There are somewhere between 150 and 200 species of Candida, speciation being performed by conventional mycologic methods, manual and automated commercial systems, and newer molecular analyses.18 Common pathogens include: C. albicans Rosen(~75% of all pathogenic isolates), C. glabrata, C. tropicalis, C. guilliermondii , C. parapsilosis, and C. krusei. Cutaneous infection with Candida species causes many morphologically distinct entities, including: congenital candidiasis, dermal lesions associated with candida sepsis, chronic mucocutaneous candidiasis, candida onychomycosis, paronychia, perleche, vulvovaginal candidiasis, candida balanitis, erosio interdigitale blastomycetica, diaper dermatitis, and intertriginous candidiasis. The last five of those enumerated previously are particularly amenable to topical therapy. C. albicans is the major pathogen in all types of cutaneous candidiasis throughout the world.19 Many individuals with cutaneous candidiasis have some form of underlying predisposition that must be addressed and, if possible, corrected in order to achieve maximum clinical outcome and to prevent prompt relapse. Some underlying conditions include: innate or acquired immunocompromise (including HIV/AIDS); administration of steroids, chemotherapeutic agents, or other immunosuppressive drugs; broad spectrum antibiotic treatment; endocrine disorders (eg, diabetes mellitus and Cushing’s syndrome); debilitation, immobility and malnutrition; obesity and hyperhidrosis; and prolonged occupational exposure to water (eg, bartender, maid).20
Epidemiologic Correlation with FDA-Approved Treatments
Table 1 lists the most readily available topical antifungal agents in the United States, including both prescription only and over-the-counter (OTC) formulations, along with corresponding FDA approved indications. The Table does not include the myriad of primarily OTC “peeling†agents based upon salicylic acid and other “non-specific†agents (such as selenium sulfide).
The three products solely formulated for nail application along with every topical antifungal agent in all chemical groups (excepting nystatin), are approved to deal with the most common dermatophye, T. rubrum. Most are also approved for use with the second most common causative dermatophyte, T. interdigitale. However, it behooves us to remember that FDA-approved indications listed in package insets are based entirely upon the results of pivotal trials. Just because an agent lacks an “indication†does not mean that the drug will fail. Most often, lacking an “indication†reflects the fact that too few patients in the pivotal studies yielded positive culture for the fungus that is not indicated. Another possibility is that the disease state was simply not studied, as FDA labeling was not sought. These factors create serious anomalies. For example, note the difference between FDA-approved indications for 1% naftifine cream/gel and the comparable 2% formulations. Does anyone seriously believe that increasing the concentration of active antifungal drug will lead to a reduced spectrum of activity? Clearly, 2% naftifine cream has not been “proven†effective, to the FDA’s satisfaction, in management of any dermatophytosis other than those caused by T. rubrum, even though the 1% naftifine
