The common fungal infections of the skin are dermatophytosis or “ringworm”, superficial candidiasis, and Malassezia infections. There are two growth forms of fungi, moulds, and yeasts.
Mould fungi produce thread-like hyphae that comprise chains of cells. In dermatophyte fungal infection of the skin, hair, and nails these hyphae invade keratin and are seen on microscopic examination of skin, hair, or nails from infected tissues.
Vegetative spores (conidia) develop in culture, and their distinctive shape helps to identify the different species.
Skin scrapings or clippings from infected nails can be easily taken and should always be sent to the laboratory for mycological examination and culture in any patient suspected of having a fungal infection.
In yeast infections such as those due to candida, the fungal cells are individual and separate after cell division by a process called budding.
In systemic, or deep, fungal infections subcutaneous on deep visceral structures are attacked. However skin involvement can also occur following blood stream dissemination and such lesions may provide a clue to the diagnosis.
Why should one suspect a lesion to be due to a fungus?
Clinical presentation
Fungal infections usually itch.
Those due to zoophilic (animal) fungi generally produce a more intense inflammatory response with deeper indurated lesions than fungal infections due to anthropophilic (human) species.
Some lesions, usually those on the trunk, have a prominent scaling margin with apparent clearing in the centre.
Hence the name “ringworm”. Children below the age of puberty are susceptible to scalp ringworm and anthropophilic fungi (from humans) have become common in some inner city areas.
They can also be infected with zoophilic fungi (from animals), particularly cattle, dogs, and cats.
Cattle ringworm can cause an intense inflammatory response in children, producing a “kerion” described below.
They rarely develop anthropophilic fungal infection.
Adults. From adolescence onwards infection of the feet is a common occurrence.
Tinea cruris in the groin is seen mainly in men and fungal nail infections (onychomycosis) have become particularly common.
Infection from dogs and cats with a zoophilic fungus (Microsporum canis) to which humans have little immunity can occur at any age.
A patient returned from a skiing holiday with intensely itchy “eczema”, which refused to clear.
A stray kitten, mewing outside in the dark, had been taken indoors, warmed in their sleeping bags, and infected the whole party with M. canis.
Nail infections
These occur mainly in adults, usually in their toenails, especially when traumatisedfor example the big toes of footballers.
The nails become thickened and yellow and crumble, usually asymmetrically.
The changes occur distally and move back to the nailfold.
In psoriasis of the nail the changes occur proximally and tend to be symmetrical and are associated with pitting and other evidence of psoriasis elsewhere.
Chronic paronychia occurs in the fingers of individuals whose work demands repeated wetting of the hands: housewives, barmen, dentists, nurses, and mushroom growers, for example.
Other predisposing factors include diabetes, poor peripheral circulation, and removal of the cuticle.
There is erythema and swelling of the nail fold, often on one side with brownish discoloration of the nail. Pus may be exuded.
The cause is Candida albicans (a yeast) together with secondary bacterial infection.
Pushing back the cuticles should be avoided—this is commonly a long term condition, lasting for years.
The hands should be kept as dry as possible, an azole lotion applied regularly around the nail fold, and in acute flares a course of erythromycin prescribed.
Feet
Tinea pedis, or athletes foot, is a common disease and its prevalence increases with age. It is easily acquired in public swimming pools or showers and industrial workers appear to be particularly predisposed to this infection.
The hands may be affected.
In interdigital tinea pedis the itching, macerated skin beneath the toes is familiar, but when a dry, scaling rash extends across the sole and dorsal surface of the foot (dry type tinea pedis) the diagnosis may be missed.
The condition needs to be differentiated from psoriasis and eczema.
Hands
Dermatophyte infections often produce a dry rash on one palm.
There may be a well defined lesion with a scaling edge.
Trunk
Tinea corporis presents with erythema and itching and a well defined scaling edge.
In the groin, tinea cruris, the infection may spread to the adjacent skin on the thighs and abdomen.
Intense erythema and satellite lesions suggest a candida infection.
In the axillae erythrasma due to Corynebacterium minutissimum is more likely.
It does not respond to antifungal treatment but clears with tetracycline by mouth.
Tinea versicolor affects the trunk, usually of fair skinned individuals exposed to the sun.
It affects mainly the upper back, chest, and arms. Well defined macular lesions with fine scales develop, which tend to be white in suntanned areas and brown on pale skin.
It may be confused with seborrhoeic dermatitis, pityriasis rosea, and vitiligo.
In skin scrapings the causative organisms, Malassezia spp., normally found in hair follicles, can be readily seen.
Scalp and face
Scalp ringworm in children may be caused by anthropophilic fungi such as Trichophyton tonsurans, which is spreading in cities in the United Kingdom, or Microsporum audouinii.
Sporadic cases are caused by M.canis which is acquired from cats or dogs.
In all cases there is itching, hair loss, and some degree of inflammation which is worse with M. canis infections.
Kerion, an inflamed, boggy, pustular lesion, is often due to cattle ringworm and is fairly common in rural areas.
It is often seen in children in the autumn when the cows are brought inside for the winter.
Tinea incognito is the term used for unrecognised fungal infection in patients treated with steroids (topical or systemic).
The normal response to infection (leading to erythema, scaling, a raised margin, and itching) is diminished, particularly with local steroid creams or ointments.
The infecting organism flourishes, however, because of the host’s impaired immune response shown by the enlarging, persistent skin lesions.
The groins, hands, and face are sites where this is most likely to occur.
Seborrhoeic dermatitis of adults may also be caused by Malassezia.
Yeast infections
Candida infection may occur in the flexures of infants and elderly or immobilised patients, especially below the breasts and folds of abdominal skin.
It needs to be differentiated from:
(a) psoriasis, which does not itch;
(b) seborrhoeic dermatitis, a common cause of a flexural rash in infants; and
(c) contact dermatitis and discoid eczema, which do not have the scaling margin.
Candida intertrigo is symmetrical and “satellite” pustules or papules outside the outer rim of the rash are typical.
Yeasts, including Candida albicans, may be found in the mouth and vagina of healthy individuals.
Clinical lesions in the mouth white buccal plaques or erythema may develop.
Predisposing factors include: general debility, impaired immunity (including AIDS), diabetes mellitus, endocrine disorders, such as Cushing’s syndrome, and corticosteroid treatment.
Vaginal candidosis or thrush is a common infection of healthy young women; an underlying predisposition is rarely found.
The infection presents with itching, soreness, and a mild discharge.
Deep fungal infection
Fungal infections of the deeper tissues are only rarely associated with skin lesions in the United Kingdom, except in patients with AIDS.
Some infections that involve deep tissue, histoplasmosis, cryptococcosis, and infections due to Penicillium marneffei, can present with skin lesions.
In an HIV positive patient lesions resembling molluscum contagiosum may be the earliest feature of deep fungal infections.
In tropical countries deep fungal infections are more common.
They should be considered in any patient from a tropical country with chronic indurated and ulcerating lesions.
Treatment
Topical treatment
The most commonly used treatments are the imidazole preparations, such as clotrimazole and miconazole (two to four weeks) and also topical terbinafine (one to two weeks).
The polyenes, nystatin, and amphotericin B are also effective against yeast infection.
For damp macerated skin dusting powders may be helpful.
In toe web infections a mixture of micro-organisms including dermatophytes and Gram negative bacteria may be present and both require treatment.
Systemic treatment
It is important to confirm the diagnosis from skin scrapings before starting treatment.
Terbinafine is a very effective fungicidal drug.
It is taken in a dosage of 250 mg once daily for two to six weeks for skin infections, six weeks for finger nail or three months for toenail infections.
It is only approved for use in children in some countries.
Blood monitoring is only advised in patients with liver disease or impaired renal function.
Pregnancy and lactation are relative contraindications.
There have been reports of headaches, taste disturbances and, very rarely, liver dysfunction.
Triazole preparations such as itraconazole are effective in both dermatophyte and yeast infections.
Cases of liver damage have rarely been reported.
Fluconazole is effective in yeast infections.
Some drugs interact with azole drugs, the main ones being terfenadine, astemizole, digoxin, midazolam, cyclosporin, tacrolimus, and anticoagulants.
Griseofulvin is mainly used for tinea capitis.
The duration of treatment is six to eight weeks for infections of the scalp.
The dose is 10–20 mg/kg for children, taken with food.
Contraindications to griseofulvin are severe liver disease and porphyrias.
The drug interacts with the coumarin anticoagulants. In countries without access to these drugs simple measures such as antiseptic paints Neutral Red or Castellan’s paint can be used. Whitfield’s ointment (benzoic acid ointment) is easily prepared and is reasonably effective for fungal infections.
