- Be able to identify and manage common dermatophyte and yeast skin infections.
- Be familiar with the range of appearance of fungal infections.
- Dermatophytes (tinea) are Trichophyton, Microsporum and Epidermophyton species.
- Tinea pedis is most frequently due to Trichophyton rubrum, T. Interdigitale or Epidermophyton floccosum.
- Fungal nail infections are often confused with psoriatic nail dystrophy.
- Zoophilic ectothrix hair shaft infections such as Microsporum canis fluoresce with Wood's light examination.
- Anthropophilic endothrix hair shaft infections such as T. tonsurans and T. violaceum can be contracted from an asymptomatic carrier.
- Confirm the presence of dermatophyte infection prior to treatment by sending scrapings and nail clippings for KOH microscopy and fungal culture.
- Predisposing factors for candidiasis include general debility, immune suppression due to disease or drugs, broad-spectrum antibiotics, high oestrogen contraceptive pill or pregnancy, diabetes mellitus and iron deficiency. Local factors include humidity, occlusion and an underlying skin disease.
- Proliferation of malassezia species results in relatively non-pruritic and flaky skin rashes.
- Malassezia has characteristic "spaghetti and meatballs" microscopy but is difficult to culture.
Fungi are classified according to the appearance of microscopy and in culture, and by the method of reproduction.
Growing fungi have branched filaments called hyphae, which make up the mycelium (like branches are part of a tree). Some fungi are compartmented by cross-walls (called septae). Arthrospores are made up of fragments of the hyphae, breaking off at the septae. Asexual spores (conidia) form on conidiophores. The sexual reproductive phase of many fungi is unknown; these are fungi imperfecta.
Yeasts form a subtype of fungus characterised by clusters of round or oval cells. These bud out similar cells from their surface to divide and propagate.
Superficial fungal infections affect the outer layers of the skin, the nails and hair. The main groups of fungi causing superficial fungal infections are:
- Dermatophytes of the genera Trichophyton, Microsporum and Epidermophyton, which cause tinea
- Yeasts especially Candida and Malassezia species
- Moulds such as Fusarium species.
Dermatophyte infections (tinea)
Tinea infections are named according to the site affected. The most common presentations are:
- Tinea pedis
- Tinea unguium
- Tinea capitis
- Tinea corporis
- Tinea cruris
Tinea pedis is most frequently due to Trichophyton rubrum, T. Interdigitale or Epidermophyton floccosum. Tinea pedis has various patterns and may affect one or both feet.
- Chronic hyperkeratotic tinea refers to patchy fine dry scaling on the sole of the foot
- Moccasin tinea is hyperkeratotic tinea affecting the skin of the entire sole, heel and sides of the foot
- Athlete's foot refers to moist peeling irritable skin between the toes, most often in the cleft between the fourth and fifth toes, and often associated with bacterial infection and irritant dermatitis
- Clusters of blisters or pustules on the sides of the feet or insteps are confused with pompholyx eczema
- Round dry patches on the top of the foot may appear similar to psoriasis
Tinea pedis is more common in adults than in children and frequently recurs after initially successful treatment with topical antifungal agents because of reinfection. Fungal spores can persist for months or years in bathrooms, changing rooms and around swimming pools.
Cluster of blisters
Moccasin tinea pedis
Athlete's foot with pseudomonas infection
Athlete's foot due to tinea in a diabetic patient
Tinea unguium is most often due to T rubrum and T. mentagrophytes var interdigitale spread from tinea pedis. Fungal nail infections (onychomycosis) may also be due to yeasts or moulds. It is particularly prevalent in the elderly. Tinea unguium may affect one or more toenails and/or fingernails and most often involves the great toenail or the little toenail. It is often confused with non-infected nail dystrophy due to skin disease, particularly psoriasis.
It can present as several different patterns:
- Lateral onychomycosis. A white or yellow opaque streak appears at one side of the nail.
- Subungual hyperkeratosis. Scaling occurs under the nail.
- Distal onycholysis. The end of the nail lifts up. The free edge often crumbles.
- Superficial white onychomycosis. Flaky white patches and pits appear on the top of the nail plate.
- Proximal onychomycosis. Yellow spots appear in the half-moon (lunula).
- Complete destruction of the nail.
Superficial white onychomycosis
Total nail destruction
Tinea capitis most often presents in young children. In New Zealand, the zoophilic dermatophyte Microsporum canis has traditionally been the cause of tinea capitis and is due to contact with an infected kitten or rarely an older cat or dog. However in the last decade, T. tonsurans and T. violaceum have also become common causes of tinea capitis; these are anthropophilic organisms, ie they naturally infect human. Anthropophilic tinea capitis may result in asymptomatic carriage in adults and children and can be transmitted by sharing hairbrushes and clothing.
Tinea capitis is classified according to how the fungus invades the hair shaft.
- Ectothrix infection (M. canis): hyphae and arthroconidia cover the outside of the hair. Ectothrix infections fluoresce green on Wood's light examination (long wave ultraviolet light).
- Endothrix infection (T. tonsurans, T. violaceum): The hair shaft is filled with hyphae and arthroconidia. Endothrix infections do not fluoresce with Wood's light.
A Wood's light is a hand-held fluorescent lamp emitting "long wave"
ultraviolet A. In dark conditions, certain infections fluoresce on exposure
to the light.
- Fungal infection due to the cat ringworm Microsporum canis fluoresces green
- Yeast infection due to certain species of malassezia (pityriasis versicolor) fluoresce yellow-green
- Bacterial infection due to erythrasma Corynebacterium minutissimum fluoresces coral-pink
As colour contrast increases on exposure to a Wood's light, the extent of pigmentary disorders can be determined.
- Vitiligo (white patches)
- Pityriasis versicolor (pale patches)
- Melasma (brown patches)
Characteristic urinary fluorescence is also helpful in the diagnosis of hepatic porphyrias (porphyria cutanea tarda).
Tinea capitis may present in several ways.
- Dry scaling - like dandruff but usually with moth-eaten hair loss
- Black dots - the hairs are broken off at the scalp surface, which is scaly
- Smooth areas of hair loss
- Kerion - very inflamed mass, like an abscess and may result in permanent scarring
- Carrier state - no symptoms and only mild scaling
Tinea capitis due to M. canis
Tinea corporis due to T. rubrum
Tinea cruris due to E. floccosum
Kerion due to T. verrucosum in cattle farmer
Tinea corporis presents as one or more round or oval erythematous scaly plaques that slowly enlarge. The term "ringworm" refers to the tendency for an annular raised edge and central healing. T. rubrum is the most common cause in New Zealand. Infection often originates as tinea pedis or tinea unguium.
M. canis from cats and T. verrucosum, from cattle tend to cause more acute tinea corporis including kerion (inflammatory abscess).
Tinea cruris refers to groin infection and is most often seen in adult men. In New Zealand, T. rubrum and E. floccosum are the usual causes, spread from the feet or nails. The rash has a scaly raised red border that spreads asymmetrically down the inner thighs from the inguinal folds or scrotum and is frequently very itchy. Tinea cruris may form ring-like patterns on the buttocks. It is not often seen on the penis or vulva or around the anus.
Diagnosis of dermatophyte infections
To establish or confirm the diagnosis of a fungal infection prior to treatment, skin, hair and nail tissue is collected for microscopy and culture (mycology).
- Scrapings of scale are best taken from the leading edge of the rash after the skin has been cleaned with alcohol. Gently remove the surface skin using a blade or curette and place in a sterile container or a black paper envelope.
- If it isn't scaly, it isn't a fungal infection!
- Strip off surface skin with adhesive tape, which is then stuck on a glass slide.
- Gently pull out infected hair.
- Use a toothbrush to collect scale from infected scalp
- Nail clippings should include debris scraped from under the distal end of an infected nail and scrapings of the surface of the nail plate.
In the mycology laboratory, the material is examined using potassium hydroxide (KOH) to dissolve keratinocytes, then staining the preparation with blue or black ink to identify KOH-resistant mycelium and arthrospores by direct microscopy. Fungal elements are sometimes difficult to find, especially if the tissue is very inflamed, so a negative result does not rule out fungal infection.
Fungal culture may take several weeks, incubated at 25-30C. The specimen is inoculated into a medium such as Sabouraud's dextrose agar containing cycloheximide and chloramphenicol. A negative culture may arise because:
- The condition is not due to fungal infection.
- The specimen was not collected properly.
- Antifungal treatment had been used prior to collection of the specimen.
- There was a delay before the specimen reached the laboratory.
- The laboratory procedures were incorrect.
- The organism grows very slowly.
Microscopy of fungal infection (M. canis)
Culture of M. canis
Wood's light on M. canis infection of scalp
Treatment of dermatophyte infections
- Keep the affected skin clean and dry. Wash daily. Dry between the toes and in the skin folds; use a hair drier if necessary.
- Clean the shower, bath and bathroom floor using bleach.
- Hot wash socks, towels and bathmats at a temperature of at least 60C.
- Avoid walking bare foot where others may tread.
- Do not share towels, sheets and personal clothing.
- Avoid long periods wearing the same clothing, or wearing occlusive clothing such as wet weather gear and nylon pantyhose.
- Wear open-toed sandals when possible. Avoid long periods in occlusive footwear such as gumboots or tramping boots.
- Use antifungal foot powder after bathing and sprinkle it in shoes.
- In the case of zoophilic fungal infections, identify and treat infected animals.
Deep fungal infections
Subcutaneous fungal infections are generally due to soil fungi that normally live on rotting vegetation. They can get pricked into the skin as a result of an injury but usually stay localised at the site of implantation. In New Zealand Pacific Islanders occasionally present with mycetoma due to eumycetes (fungi) or actinomycetes such as Nocardia species, or chromoblastomycosis caused by various dematiaceous (brown) fungi.
Candida yeasts depend on a living host for survival. C. albicans is a normal inhabitant of the human digestive tract from early infancy, where it lives without causing any disease most of the time. However, if the host's defences are lowered, C. albicans and other Candida species can cause infection of the mucosa (the lining of the mouth, anus and genitals), the skin, and rarely, deep-seated infection.
Candidal skin infections include:
- Oral candidiasis (oral thrush)
Oral candidiasis with angular cheilitis
- Intertrigo (skin fold infections)
- Vulvovaginal candidiasis (genital infection in women) including cyclic vulvovaginitis
- Balanitis (penile infection)
- Napkin dermatitis
Candidal napkin dermatitis
- Chronic paronychia (nail fold infection)
Chronic paronychia and onychomycosis
- Chronic mucocutaneous candidiasis
Characteristically candida causes red and white patches on mucosal surfaces. In skin folds it results in moist fissuring with satellite superficial papulopustules.
Refer to DermNet. for further information about each of these presentations.
Predisposing factors for infection include:
- Infancy or old age
- Warm climate
- Occlusion e.g. plastic pants (babies), nylon pantyhose (women), dental plates
- Immune deficiencies e.g. low levels of immunoglobulins, infection with human immunodeficiency virus (HIV)
- Broad spectrum antibiotic treatment
- High oestrogen contraceptive pill or pregnancy
- Chemotherapy or immunosuppressive medications such as systemic steroids
- Diabetes mellitus, Cushing's syndrome and other endocrine conditions
- Iron deficiency
- General debility e.g. from cancer or malnutrition
- Underlying skin disease e.g. psoriasis, lichen planus
Microscopy and culture of skin swabs and scrapings id in the diagnosis of candidiasis. However, candida can live on a mucosal surface quite harmlessly. It may also secondarily infect an underlying skin disorder such as psoriasis; thus positive culture does not always mean a dermatosis is candidiasis.
Malassezia species may be identified in apparently normal skin. There is some controversy as to whether specific species cause different skin diseases.
Several skin conditions are associated with proliferation of malassezia, especially with predisposing factors humidity, sweating and seborrhoea. They include:
- Pityriasis versicolor (asymptomatic pink, white or brown scaly patches on the trunk)
- Malassezia folliculitis (superficial acne-like rash on upper trunk)
- Pityriasis capitis (dandruff)
- Seborrhoeic dermatitis (non-pruritic scaly red patches on face, scalp and flexures)
Facial seborrhoeic dermatitis
Axillary seborrhoeic dermatitis
- Facial atopic dermatitis, in some cases.
The diagnosis of malassezia infections is made from skin scrapings. Microscopy of potassium hydroxide (KOH) preparations shows clusters of yeast cells and long hyphae. The appearance is sid to be like "spaghetti and meatballs". Malassezia species are difficult to grow in the laboratory so scrapings may be reported as culture negative. The yeast grows best if olive oil is added to the culture medium.
Culture of C. albicans
Microscopy of malassezia