Superficial & Cutaneous Mycoses

Basidiomycota: Specifically, species of Malassezia, which are yeast that colonize the superficial layers of the skin and hair. Because they do not invade or destroy living tissues, they generally do not trigger an immune response. Infections common in warm, moist environments. Ascomycota: Dermatophytes are fungal pathogens that can invade the skin and cause dermatophytoses, such as ringworm. Dermatophytic species come from three genera: Trichophyton, Epidermophyton, and Microsporum. These molds infect keratin of the skin, hair, and nails; because they cause damage to the tissues, they trigger an immune response. These fungi cause mycoses called tineas, aka, ringworm. They are acquired from contact with infected soil, animals, or other humans. KOH (potassium hydroxide) testing, in which skin scrapings and KOH are viewed under microscope. Calcofluor white stain is also used to detect fungi in samples; comprises fluorescent stain with affinity for the chitin in fungal cell walls. When necessary, treatments for superficial and cutaneous mycoses involves topical and/or oral antifungals, in addition to good hygiene. Sometimes called tinea versicolor. Caused by species of the Malassezia genus. Malassezia comprises cells and some short hyphae; some authors describe their appearance as looking like "spaghetti and meatballs." Young adults in warm, moist environments are most likely to develop pityriasis versicolor. Fungi are spread via human to human contact. Lesions appear as either hypo- or hyper-pigmented, and typically appear on the upper body, face, and neck. Tinea nigra is caused by the fungus Hortaea werneckii. Comprises septate hyphae and budding cells. Tinea nigra is most common in children and young adults in tropical and subtropical climates. Manifests as patches of small dark dots, typically on the palms of the hands and soles of the feet. White piedra (piedra means "stone") is caused by species of Trichosporon, which are yeasts that colonize the hair shaft. Individuals in tropical and subtropical areas are most likely to have white piedra. Look for soft white or cream-colored nodules on the hair shafts. Black piedra is caused by the yeast Piedra hortae, which colonizes the hair and scalp of individuals in tropical areas. Look for firm dark nodules in the hair. ___________________________________________________________________ ___________________________________________________________________ Commonly referred to as Ringworm. Caused by dermatophytic fungi. The tineas are named for their location on the body, as follows: Tinea capitis develops on the scalp, especially of children, and is associated with alopecia, scaling, and cervical and suboccipital lymphadenopathy. Tinea barbae is ringworm that occurs in areas of facial hair. Tinea corporis is ringworm that appears on the trunk or extremities; it produces red rings with scaly skin and is pruritic (itchy). Tinea cruris, aka, jock itch, is most common in adolescent and young males; it produces a rash on the upper thighs, but typically does not involve the scrotum. Tinea pedis, aka, athlete's foot, can involve all aspects of the feet: Interdigital is the most common, and involves the skin between the toes Moccasin tinea pedis is chronic and involves the sides and soles of the feet Vesicular tinea pedis is characterized by inflammation with vesicles and lesions Tinea unguium is a fungal infection of the nails (thus, it is a type of onychomycosis). Be aware that opportunistic fungi that infect the skin, such species of Candida, are discussed in separate tutorials.