Superficial and cutaneous mycoses Flashcards
Characteristics of superficial mycoses (6)
- Non-invasive, asymptomatic
- Little to no inflammation
- Found most frequently in tropical climates
- Involves keratin-containing layers of skin or hair
- Aesthetically displeasing
- Specimens: skin scrapings or plucked hairs
Which organ is most commonly affected by fungal infections?
The skin
Dermatophytes causing fungal infections of the hair and nails (3)
- Trichophyton sp.
- Epidermophyton sp.
- Microsporum sp.
Malassezia
Lipophilic, part of the normal skin microbiota in 97% of humans and in animals. Common infections in patients living in warm, humid climates. T cell deficiencies are associated with significant disease. Basidiomycota yeasts- most commonly viewed in samples as blastospore form.
Malassezia species (7)
- Malassezia furfur
- Malassezia obtusa
- Malassezia sympodialis
- Malassezia globosa
- Malassezia slooffiae
- Malassezia pachydermatis
- Malassezia restricta
Pityriasis (Tinea) versicolor
Chronic skin infection caused by Malassezia species. Patients have white, pink, or brown hypopigmented or hyperpigmented lesions. The lesions are on the upper trunk, neck, shoulders and arms, rarely on face, and are often merging, covered with thin flaky scales. Fluoresce a pale greenish color under ultra-violet light. Young adults most often affected, but the disease may occur in childhood and the elderly.
Pityriasis (Tinea) folliculitis
Caused by Malassezia species. Pruritic, follicular papules and pustules on the upper back and shoulders. Less common on face and neck. The lesions are itchy and often appear after sun exposure. Diagnosed through skin scrapings or biopsy specimens
Pityriasis (Tinea) folliculitis diagnosis
Microscopic - numerous yeasts, short septate hyphae around the infected follicles. Calcofluor white is used. Culture is not required due to scant growth-diagnosis is made from microscopic and patient signs and symptoms
Seborrheic dermatitis
Caused by Malassezia species- leads to dandruff (mildest form of infection) or cradle cap in infants. Common symptoms include pruritic red patches with greasy scales on the scalp- may include eyebrows, nasolabial folds, ears, axilla or groin. Scalp itching is common. Laboratory diagnosis is made through skin scraping and patient signs and symptoms, culture not required
Direct microscopy diagnostic for Malassezia species
10% KOH and stain are added to skin scrapings. Clusters of thick-walled round, budding yeast-like cells and short-septate hyphal forms (NOT pseudohyphae) are observed, approximately 4µm in diameter. “Spaghetti and meatballs” morphology
White piedra
An infection of the hair shaft caused by Trichosporon species. Patients exhibit irregular, soft, white or light brown nodules, 1.0-1.5 mm in length, firmly adhering to the hair. Most commonly occurring on head, or may be isolated from facial or pubic hair. Common in young adults. Have true hyphae, pseudohyphae, arthroconidia, Blastoconidia
Trichosporon species
This pathogen is found worldwide and is most common in tropical or subtropical regions. It is part of the normal skin microbiota and is widely distributed in nature. Causes white and black piedra and opportunistic infections in the immunocompromised. Disseminated infections are most frequently (75%) caused by Trichosporon asahii. At risk populations- leukemia, organ transplantation, multiple myeloma, aplastic anemia, lymphoma, solid tumors and AIDS.
Piedraia hortae
Infection of the hair shaft that causes black piedra. The nodules exhibit true hyphae that are brown (dematiaceous)- there are masses of intertwined hyphae and ascospores. Most common in tropical South and Central America, Southeast Asia and Africa. Part of the normal skin microbiota and widely distributed in nature.
Tinea nigra
Superficial, asymptomatic skin infection caused by Hortaeawerneckii. Patients may exhibit flat, smooth lesions on the palms of the hands. Most common in tropical South and Central America, Southeast Asia and Africa
Tinea nigra morphology
Examination of brown-pigmented skin scraping shows
true hyphae and budding yeast cells. In culture, growth is a black yeast colony, which is unusual. It takes 21 days for growth
Characteristics of cutaneous mycoses (6)
- Dermatomycoses
- Affect deeper epidermal layers of skin
- Produce more tissue destruction and symptoms
- Tinea- ringworm
- Found in soil (geophilic), animals (zoophilic), and humans (anthropophilic)
- Specimens: nail scrapings, skin scrapings, and hair stubs with roots
Characteristics of dermatophytes (4)
- Infect hair, skin and nails
- Breakdown and utilize keratin as nitrogen and carbon source
- Organisms do not penetrate subcutaneous tissues
- Resistant to cyclohexamide and chloramphenicol
Tinea
Also called ringworm, patients exhibit circular, scaly patches resembling a worm below the surface of the skin. Contagious, the infection spreads from person to person. It can occur in various parts of the body, but tinea pedis (athlete’s foot) is the most common. Trichophyton mentagrophytes is the most common cause
Tinea corporis
Ringworm of the body- dermatophytosis of glabrous skin of the face, trunk and limbs, excluding the beard. It has worldwide distribution, with the highest prevalence in warm, humid climates. There is no preference for gender or age. Presents noninflammatory oval to round lesions to scaly plagues, hair follicle involvement, bacterial infections. Geophilic/Zoophilic –inflammatory, pustules, vesicles. Diagnosed by KOH-Calcofluor smear and culture
Tinea pedis
Also called athlete’s foot, most common ringworm infection. There are 4 presentations. More common in males, and with increasing age- 70% of population has been infected at least once. Commonly found with Tinea manuum. Chronic infection results with nail involvement is called onychomycosis. Diagnosed using a KOH-Calcofluor smear, culture would be confirmatory only.
