Cutaneous Mycoses: Tinea Pedis and Corporis

• Cutaneous mycoses are common skin diseases which are caused by dermatophytes
• Dermatophytes are a group of related fungi
• Dermatophytes infect keratinized tissues like skin, hair, and nails
• Dermatophytes cause superficial fungal infections
• There are 3 genera of dermatophytes, each with many species:
  • Trichophyton
  • Epidermophyton
  • Microsporum

Tinea Pedis (Athlete's Foot)

• Most often isolated fungi include:
  • Trichophyton rubrum
  • Trichophyton mentagrophytes
  • Epidermophyton floccosum
• Initially infects tissue between the toes which can then spread to the nails
• The nails become yellow and brittle
• Skin fissures can lead to secondary bacterial infections and lymph node inflammation

Tinea Corporis (Ringworm)

• Most often isolated fungi include Epidermophyton, Trichophyton, and Microsporum.
• Lesions appear as advancing rings with scaly centers.
• The periphery of the ring is usually inflamed and vesiculated
• Lesions most often occur on non-hairy areas of the trunk, including the iliac side

Tinea Capitis (Scalp Ringworm)

• Several species of Trichophyton and Microsporum are isolated from scalp ringworm lesions
• In the US, the predominant infecting species is Trichophyton tonsurans
• Disease manifestations range from small scaling patches to involvement of the entire scalp with extensive hair loss
• Hair shafts can become infected by Microsporum hyphae, demonstrated by green fluorescence under Wood's lamp

Tinea Cruris (Jock Itch)

• Causative organisms: Epidermophyton floccosum and Trichophyton rubrum
• Lesions occur in moist, groin areas, and can spread from the upper thigh to the genitals

Tinea Unguium (Onychomycosis)

• Caused by Trichophyton rubrum
• Nails become thick, discolored, and brittle
• Treatment must continue for 3-4 months until all infected portions of the nail have grown out

Transmission of Dermatophytes

• Transmitted from human to human or animal to human
• Transmitted by infected skin via scales on inanimate objects

Characteristics of Dermatophytes

• Defining characteristic is the ability to use keratin as a source of nutrition
• Can invade keratinized tissues and structures such as skin, hair, and nails
• Does not invade underlying non-keratinized tissue
• Characterized by itching, scaling skin patches that can become inflamed and vesicular/weeping
• Specific diseases are usually identified according to the affected tissue, such as the scalp, pubic area, or feet

Treatment for Dermatophytosis

• First course of treatment involves removal of infected skin
• Followed by topical application of antifungal drugs like itraconazole and clotrimazole
• Can also be treated via oral treatments like terbinafine and griseofulvin
• Terbinafine is the drug of choice for onychomycosis