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Chapter 160: Superficial Fungal Infection

Lauren N. Craddock; Stefan M. Schieke

AT-A-GLANCE

AT-A-GLANCE

  • Mycoses are divided among 3 forms: superficial, subcutaneous, and deep/systemic.

  • Superficial fungal infection is defined as a dermatophyte infection of keratinized tissues including skin, hair, and nails.

  • Dermatophyte species are contained in 3 genera (Epidermophyton, Microsporum, and Trichophyton), which are further divided according to 3 natural habitats (humans, animals, and soil).

  • Trichophyton is the most common genera isolated in the United States.

  • Trichophyton rubrum is the most common cause of dermatophytosis of the skin.

  • Trichophyton tonsurans is the most common cause of tinea capitis in the United States.

  • Piedra, which consists of white and black forms, is an asymptomatic superficial fungal infection of the hair shaft.

  • Onychomycosis is the name given to dermatophytosis of the nails.

  • Microscopic examination, culture, Wood light evaluation, and histopathology may all be useful in confirming diagnosis.

  • Several topical and oral antifungals are available for effective treatment of dermatophytosis.

  • Infections involving hair bearing skin and nails typically require oral treatment.

MYCOSES

Mycoses are divided among 3 forms: (a) superficial, involving stratum corneum, hair, and nails; (b) subcutaneous, involving dermis and/or subcutaneous tissue; and (c) deep/systemic, representing hematogenous spread of organisms including opportunistic pathogens in immunocompromised hosts. This chapter focuses on the superficial mycoses and their patterns of integumentary infections (Table 160-1). Table 160-2 is a glossary of terms used in this chapter.

Table 160-1Patterns of Integumentary Infections by Superficial Mycoses
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Table 160-1 Patterns of Integumentary Infections by Superficial Mycoses
GENERA SKIN HAIR NAILS
Trichophyton × × ×
Microsporum × ×  
Epidermophyton ×   ×
Tinea nigra ×    
Black piedra   ×  
White piedra   ×  
Table 160-2Glossary of Terms
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Table 160-2 Glossary of Terms

  • Anthropophilic—preferring humans over other animals as the natural habitat.

  • Arthroconidia—asexual spore produced by segmentation of hyphae.

  • Dematiaceous—melanin in the cell walls of its conidia, hyphae, or both results in a darkly colored fungus.

  • Ectothrix—dermatophyte growth pattern with spores forming a sheath on the outside of the hair shaft.

  • Endothrix—dermatophyte growth pattern with spore formation within the hair shaft.

  • Favus—dermatophyte growth pattern with hyphae and air spaces within the hair shaft.

  • Geophilic—preferring the soil over humans and animals as natural habitat.

  • Hyphae—long, filamentous fungus cells forming a branching network called mycelium.

  • Macroconidia—asexual large multinucleate spores produced by vegetative reproduction.

  • Microconidia—asexual small spores produced by vegetative reproduction.

  • Zoophilic—preferring animals over humans as the natural habitat.

DERMATOPHYTES

The kingdom of fungi comprises more than 1.5 million species worldwide. Dermatophytes (the term is derived from the Greek words for “skin plant”) are represented by approximately 40 species divided among the 3 genera Trichophyton, Microsporum, and ...

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