- Superficial fungal infections are caused by numerous fungi that are capable of superficially invading the following:
- Hair/hair follicles
- Nail apparatus
- Mucosal sites
- These fungi are commensural organisms that frequently colonize normal epithelium.
- Candida species
- Malassezia species
- Infections can extend more deeply in the immunocompromised host.
- Deeper, chronic cutaneous fungal infections can occur after cutaneous inoculation.
- Systemic fungal infections with cutaneous dissemination; these infections occur most often in the immunocompromised host.
- Primary lung infection; can disseminate hematogenously to multiple organ systems, including the skin.
- North American blastomycosis
- Primary gastrointestinal (GI) infection; neutropenic host
- Disseminated candidiasis commonly arises in the GI tract.
ICD-9 : 111 • ICD-10 : B36
- Superficial fungal infections are the most common of all mucocutaneous infections, often caused by overgrowth of transient or resident flora associated with a change in the microenvironment of the skin.
- Fungi causing these infections:
- Dermatophytes: infect keratinized epithelium, hair follicles, and nail apparatus
- Candida spp.: Require a warm humid envir-onment.
- Malassezia spp.: Require a humid microenvironment and lipids for growth.
- Trichosporon spp
- Hortaea (Exophiala or Phaeoannellomyces) werneckii: Tinea nigra
ICD-9 : 110 • ICD-10 : B35.0-B36
- Dermatophytes are a unique group of fungi capable of infecting nonviable keratinized cutaneous structures including stratum corneum, nails, and hair.
- Dermatophytosis denotes an infection caused by dermatophytes.
- Clinical infection by structure involved:
- Epidermomycosis (epidermal dermatophytosis)
- Trichomycosis (dermatophytosis of hair and hair follicles)
- Onychomycosis (dermatophytosis of the nail apparatus)
- The pathogenesis of epidermomycosis vs trichomycosis leading to different clinical manifestations is schematically depicted in 5194081.
- The term tinea is best used for dermatophytoses and is modified according to the anatomic site of infection, e.g., tinea pedis.
- “Tinea” versicolor is called pityriasis versicolor outside of the United States; it is not a dermatophytosis but rather an infection caused by the yeast Malassezia.
The pathogenesis of epidermomycosis (A) and trichomycosis (B) are different because they involve different structures leading to different clinical manifestations. In epidermomycosis, dermatophytes (red dots and lines) within the stratum corneum not only disrupt the horny layer and thus lead to scaling, but also elicit an inflammatory response (black dots symbolize inflammatory cells), which may then manifest as erythema, papulation, and even vesiculation. On the other hand, in trichomycosis the hair shaft is involved (red dots) resulting in the destruction and breaking off of the hair. If the dermatophyte infection extends farther down into the hair follicle, it will elicit a deeper inflammatory response (black dots) and this will manifest as deeper inflammatory nodules, follicular pustulation, and abscess formation. (See also Fig. 25-19.)
Epidemiology and Etiology