Dermatophytes or ringworm fungi are able to invade the keratinized tissue of the skin, nails or hair and include Epidermophyton, Microsporum or Trichophyton. The term ‘tinea’ means ‘moth-eaten’ and may be used to denote the pattern of involvement, e.g. tinea capitis.
The source of the fungus may be zoophilic (animal to man), anthrophilic (human to human) or geophilic (soil to man).
Scrapings taken from the skin and dissolved in 20% potassium hydroxide should reveal the presence of
hyphae. A second sample is plated on a culture medium and incubated. Samples from nail clippings and hairs may be analysed in the same way.
This is now an uncommon disease in the UK. The organism most commonly involved is Microsporum canis, which is transmitted from the coats of dogs and cats.
Areas of scaling and hair loss are evident in children infected by M. canis, but at puberty changes within the hair itself limit infection. On occasions more marked inflammatory changes are seen with a boggy swelling in the scalp, surmounted by crusting and loss, or matting, of the hair; this is called kerion. Scarring of the scalp that may follow such infection can lead to permanent hair loss.
Trichophyton species, T. tonsurans and T. violaceum, invade the hair shaft (endothrix) and often cause the hair to break off at the level of the scalp, producing a black dot appearance. More widespread and severe hair loss, associated with a characteristic pattern of scaling in which yellowed keratin scale passes upwards along the hair shaft forming a scutulum or ‘shield’ shape, is seen with the infection favus, which is caused by T. schoenleinii. This infection is seen in the Middle East, southern Africa, Greenland and, less frequently, in Pakistan.
Examination by Wood’s light produces a greenish fluorescence of the scalp when it is infected with M. canis and other species that invade the surface of the hair (ectothrix).
It is important to treat the animal source of infection. Spread from human to human is unusual with infection produced by M. canis. Griseofulvin is given by mouth and treatment may need to be prolonged for up to 3 months. Itraconazole is also being used. Antibacterial treatment may be required for suppurative disease (kerion), either topically or by mouth, in order to lessen the risk of scarring.
This refers to infection that involves principally the toe webs or the soles of the feet
The infecting organism is most commonly T. rubrum (colonies produce red coloration on culture). Epidermophyton fIoccosum and T. mentagrophytes are less commonly seen Occupations that produce maceration of the skin and communal spread include coal mining and working on submarines, where warm decks and rubber-soled shoes encourage infection. Athletic pursuits (athlete’s foot infection), the wearing of occlusive footwear and swimming also encourage spread of these infections. The disease is often intractable and T. rubrum infection may be especially difficult to eradicate, with the organism showing resistance to both topical and systemic fungicides.
Infection is mostly seen as:
• Scaling, maceration and erythema of the lateral toe webs
• Blistering lesions, often few in number on the plantar surface of the toes or foot
• Confluent erythema and scaling on the soles
Spread may occur to the palms or to the medial aspect of the thigh and perianal skin of males.
Foot powders often contain antifungal agents of low potency but their drying effect is useful when they are applied regularly. Drying foot soaks such as potassium permanganate 0.01% solution may discourage infection by preventing maceration.
Specific measures include oral griseofulvin. This may need to be given for periods of up to 3 months for disease associated with T. rubrum in doses of 500 mg twice daily. Imidazoles (clotrimazole or miconazole) can be applied overnight as a cream and used as a talc in powder form by day.
This most commonly affects the great-toe nails but several nails may be affected. It causes discoloration, chalky deposits, subungual hyperkeratosis and fragmentation of the nail plate. Infected finger-nails show similar changes but are less frequently involved. Unusual trauma associated with occupations and hobbies, congenital changes or malalignment may also produce misshapen great-toe nails. When several toe-nails are involved the differential diagnosis includes psoriasis.
Clippings taken from the free edge of the nail should be sent for culture. Usually the same organisms that cause tinea pedis are found.
Nail-plate infection will require systemic treatment for up to 9 months for finger-nails and 2 years for toe-nails. Griseofulvin 0.5-1 g daily given for such a length of time is seldom associated with serious side-effects but it may fail to eradicate the infection even though the cosmetic appearance is improved. The combination of tioconazole lotion, which penetrates the nail, with griseofulvin can speed and increase the chances of clearing. Itraconazole is also used or terbinafine, an allylamine, can be given by
mouth. It has a more rapid effect clearing toe-nails in 4-6 months and the recurrence rate is less than when using griseofulvin.
Infection of the skin of the groin (tinea cruris) is not infrequently seen in males with chronic infection of the feet, so that both areas should be examined at the same time. An area of erythema and scaling is surrounded by a well-defined edge and is often studded with pustules or papules. Infection may extend over the perianal skin.
Tinea corporis may be evident in older members of the family, while children are infected on the scalp. Annular, erythematous and scaled lesions are then seen on the trunk or limbs. More inflammatory, pustular and indurated plaques affect the neck or shoulders of farm workers who come into contact with cattle infected with T. verrucosum.
Diagnosis is by direct microscopy and culture of skin scrapings. Treatment is with griseofulvin and local antifungal cream.