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Dermatophytosis

Also called tinea or ringworm, dermatophytosis is a disease that can affect the scalp (tinea capitis), body (tinea corporis), nails (tinea unguium), feet (tinea pedis), groin (tinea cruris), and bearded skin (tinea barbae).

The disease process in dermatophytosis is unique for two reasons: Firstly, no living tissue is invaded the keratinised stratum corneum is simply colonised. However, the presence of the fungus and its metabolic products usually induces an allergic and inflammatory eczematous response in the host.

The type and severity of the host response is often related to the species and strain of dermatophyte causing the infection. Secondly, the dermatophytes are the only fungi that have evolved a dependency on human or animal infection for the survival and dissemination of their species.

Tinea infections are quite prevalent in the United States and are usually more common in males than in females. With effective treatment, the cure rate is very high, although about 20% of persons with infected feet or nails develop chronic conditions

Causes

Tinea infections (except for tinea versicolor) result from dermatophytes (fungi) of the genera Trichophyton, Microsporum, and Epidermophyton.

Transmission can occur directly (through contact with infected lesions) or indirectly (through contact with contaminated articles, such as shoes, towels, or shower stalls). Some cases come from animals or soil.

Signs and symptoms

Lesions vary in appearance and duration with the type of infection:

• Tinea capitis, which mainly affects children, is characterized by round erythematous patches on the scalp, causing hair loss with scaling. In some children, a hypersensitivity reaction develops, leading to boggy, inflamed, often pusfilled lesions (kerions).
• Tinea corporis produces flat lesions on the skin at any site except the scalp, bearded skin, groin, palms, or soles. These lesions may be dry and scaly or moist and crusty; as they enlarge, their centers heal, causing the classic ring shaped appearance.
• Tinea unguium (onychomycosis) infection typically starts at the tip of one or more toenails (fingernail infection is less common) and produces gradual thickening, discoloration, and crumbling of the nail, with accumulation of subungual debris. Eventually, the nail may be destroyed completely.
• Tinea pedis causes scaling and blisters between the toes. Severe infection may result in inflammation, with severe itching and pain on walking. A dry, squamous inflammation may affect the entire sole.
• Tinea cruris (jock itch) produces red, raised, sharply defined, itchy lesions in the groin that may extend to the buttocks, inner thighs, and the external genitalia. Warm weather and tight clothing encourage fungus growth.
• Tinea barbae is an uncommon infection that affects the bearded facial area of men.

Diagnosis

Microscopic examination of lesion scrapings prepared in potassium hydroxide solution usually confirms tinea infection. Other diagnostic procedures include Wood's light examination (which is useful in only about 5% of cases of tinea capitis) and culture of the infecting organism.

Treatment

Tinea infections usually respond to topical agents such as imidazole cream or to oral griseofulvin, which is especially effective in tinea infections of the skin and hair. Oral terbinafine or itraconazole is helpful in nail infections.

However, topical therapy is ineffective for tinea capitis; oral griseofulvin for 1 to 3 months is the treatment of choice.

Tinea versicolor may be treated with selenium sulfide lotion or ketoconazole shampoo.

Prevention of Dermatophytosis