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.
Tinea manus
Ringworm of the hand
Tinea cruris
Jock itch- common in warm, tropical climates. Moisture and increase in temperature favor growth of the organism, and prolonged exposure to wet clothing increases risk. Can be spread from tinea pedis, manuum and unguium. Symptoms- redness, severe itching, and weeping lesions at the edge of inflammation are possible. KOH-Calcofluor smear & culture used for diagnosis
Tinea barbae
Ringworm of the beard
Tinea capitis
Ringworm of the scalp- a dermatophytosis of the scalp or hair follicle. Called favus if caused by Trichophyton schoenleinii. Worldwide distribution, but most commonly found in developing countries. Most common is prepubescent children (3 to 7 years old) and are equally distributed among males and females. Diagnosis is made by hair examination to determine if the infection is an ectothrix or endothrix. Cultures of skin scraping, hair often required – takes 21 days to grow
Ectothrix
Infection found around the outside of the hair shaft- the cuticle is destroyed
Endothrix
Infection found inside of the hair shaft, the cuticle is not destroyed
Types of cutaneous mycoses (3)
- Microsporum species
- Trichophyton species
- Epidermophyton species
Diagnosis of tinea
Hair will fluoresce using Wood’s lamp:
1. M. audouinii, M. canis - bright yellow-green fluorescence
2. M.gypseum - may glow slightly
3. T. tonsurans - may glow dull white
4. T. schoenleinii - may glow gray-white or bright yellow green
Sources of cutaneous mycoses (3)
- Geophilic- soil
- Zoophilic- animals
- Anthropophilic- humans
4 presentations of tinea pedis
- Moccasin (dry, scales entire plantar surface)
- Interdigital (fissuring of toe webs, 4th &5th toes)
- Inflammatory (vesicles, bulla or pustules, painful, most common in summer)
- Ulcerative (secondary bacterial infection, progression of inflammation)
3 species causing tinea pedis
- Trichophyton rubrum
- Epidermophyton floccosum
- Trichophyton mentagrophytes
Trichophyton rubrum
Causes: tinea corporis, t. pedis, t. cruris, t. unguium. The colony is granular fluffy white in front with a pink periphery. The reverse is red. It is urease negative and does not penetrate hair
Microscopic characteristics of Trichophyton rubrum
Numerous club-shaped microconidia, racquet hyphae, nodular organs. Macroconidia form on BHI
Trichophyton mentagrophytes
Causes: most common cause of tinea pedis, also causes tinea corporis, tinea unguium, tinea barbae, tinea capitis. There are two colony types: fluffy, white/ yellow reverse or granular, buff to rose-tan/ reverse- brown, red, yellow
Trichophyton mentagrophytes microscopic appearance
Round microconidia in grape-like clusters, must differentiate from T. rubrum. Macroconidia sometimes seen
Epidermophyton floccosum
Causes- tinea pedis, tinea cruris, tinea unguium. The front of the colony is khaki, yellow, velvety, and the reverse is tan
Epidermophyton floccosum microscopic appearance
There are numerous club-shaped macroconidia (beaver’s tail). Smooth, thin-walled, 2-4 cells, borne singly or clusters racquet hyphae, spiral hyphae, nodular bodies, chlamydoconidia. No microconidia
Eczema marginatum
Also called gym itch. Common on the medial upper thigh, inguinal, pubic, perineal and perianal areas. Most common in post pubertal males, rarely females
Tinea unguium
Causes Onychomycosis, an infection of the fingernails or toenails. This term applies to nail infection with any microorganism, not only fungus. 90% of these infections are caused by Dermatophytes. Incidence increases with age, ~28% of patients 60 years old and older have a culture confirmed Dx. Immune disfunction, comorbidities, and foot hygiene increase risk. There are several different types of infections. Hyperkeratosis, yellow-brown discoloration, and onycholysis are common symptoms. Differential diagnosis for Psoriasis, KOH-Calcofluor smear and culture are done for diagnosis
Risk factors of tinea corporis (4)
- Diabetes, Cushing syndrome, HIV and immunocompromised at high risk for infection.
- Outdoor occupation
- Close association with animals
- Contact sports
Microsporum canis
A zoophilic infection- the two varieties are canis and distortum. Causes: tinea corporis and tinea capitis. The infected hairs fluoresce. The front of the colony is wooly, buff to brown, bright yellow periphery. The reverse is bright yellow (yellow-orange)
Microsporum audouinii
Causes tinea corporis, tinea capitis; infected hairs fluoresce. Also known as “Grey patch ringworm”. The front of the colony is velvety, light tan. The reverse is a salmon color (esp. on PDA) later, orange-brown
Microscopic characteristics of Microsporum audouinii
Microconidia: rare, club shaped, racquet hyphae, nodular bodies. The macroconidia are rough, thick walled, 6-15 cells, spindle shaped (tapered ends). Terminal vesicles (usually pointed) seen most frequently
Microsporum gypseum
Causes inflammatory tinea corporis & tinea capitis- geophilic. The front of the colony is powdery and is a buff to cinnamon color. The reverse is tan. Microconidia- few club-shaped, borne singly along hyphae. Macroconidia- numerous thin walled elliptical
Causes of tinea capitis (2)
- Zoophilic – Microsporum canis, most common in the world
- Trichophyton tonsurans – most common in US and Western Europe
Symptoms of tinea capitis
Lesions range from dry and scaly patches of alopecia to inflammatory pustules. Cervical lymphadenopathy is common. Systemic drug treatment is often necessary
Trichophyton schoenleinii
Causes favus, tinea capitis, rarely tinea corporis or tinea unguium. The front of the colony is waxy, heaped, and a yellow to buff color. The reverse is colorless to yellow-orange. Microscopic- very rare microconidia or macroconidia. Exhibits chlamydoconidia with hyphal swellings and favic chandeliers
Trichophyton tonsurans
Causes: black dot tinea capitis, tinea corporis, tinea pedis, tinea unguium. Sometimes severe with erythema nodosum.
3 colony types of Trichophyton tonsurans
- grey-white suede/mahogany reverse
- granular white/colorless reverse
- granular to suede, rugose/yellow reverse
Microscopic characteristics of Trichophyton tonsurans
Microconidia- numerous, great size & shape variation. Macroconidia- rare, smooth, club-shaped
Trichophyton tonsurans tests for diagnosis (4)
- Trichophyton agars
- Urease + within 4 days
- Endothrix
- Grows better in thiamine
Trichophyton violaceum
Causes tinea capitis, tinea corporis, rarely, tinea unguium. The front of the colony is waxy, suede, and violet heaped. The reverse is lavender. Microscopic- no macroconidia, microconidia- chlamydoconidia with hyphal swellings. Other characteristics- requires thiamine, endothrix
