Diagnosis: Tinea pedis
Our young athlete had tinea pedis, also known as “athlete’s foot” or “foot ringworm.” Tinea pedis affects the toes and feet and is the most common fungus infection. Dermatophyte infections, such as tinea pedis, are superficial, caused by fungal organisms that live on the keratin layer of the skin and rarely invade the dermal layers. The inflammation is caused by diffusion of fungal by-products in the skin and by the host reaction to the organism and its toxins.
The condition is most common among teenagers and adults and rare in children; prevalence is higher among males. It is suggested that 10% of the total population has clinical tinea pedis at one time or another.
Tinea pedis presents in one of four clinical forms. Variants can occur with all four types; clinical features can overlap. Interdigital tinea pedis is the most common. Fissuring, scaling, and maceration are often seen in the interdigital or subdigital areas of the lateral toe webs, especially between the fourth and fifth toes, and may spread to the sole or instep. Many affected individuals also have hyperhidrosis. Also found in the moist environment of the toe webs are increased numbers of bacteria. Symptomatic athlete’s foot can be due to the overgrowth of both fungal and bacterial components as well as their interaction.
Chronic tinea pedis, the most difficult form to treat, presents with a dry powdery scale involving the soles and sides of the foot in a diffuse moccasinlike pattern. Nail involvement is common. In some patients, the hands are also affected (tinea manuum). A common but unexplained variant is the “two foot, one hand disease” in which one hand is totally spared.
Acute vesicular tinea pedis, more common in summer, features small vesicles or vesiculopustules on the instep and on the mid-anterior plantar surface. Bullae may also be present, and inflammation can be severe. Scaliness may be detectable in the surrounding area, and toe-web fungus is occasionally seen.
The least common form is acute ulcerative tinea pedis in which maceration, weeping denudation, and ulceration of the sole are noted. White hyperkeratosis and a pungent odor can be caused by the fungus as well as the secondary overgrowth of bacteria, usually gram-negative organisms. When associated with secondary bacterial infection, this form has been called dermatophytosis complex.
Tinea pedis is usually diagnosed clinically. Confirmation with fungal culture is reserved for nonresponding cases. The differential diagnoses for interdigital fissuring include gram-negative infection with Pseudomonas and Proteus, candidiasis, erythrasma, eczema, or soft corns. It is impossible to prevent exposure to the fungal organisms that cause tinea pedis, especially in communal baths or swimming facilities. The fungi are frequent transitory inhabitants of our normal skin flora. Fungal culture studies have shown that 80% of young adult males have potentially pathogenic fungus normally isolated on their feet.
Treatment begins with keeping the feet dry by wearing sandals, avoiding continual wearing of nonocclusive shoes, going barefoot or wearing slippers at home, changing socks frequently, and using foot powder in shoes.
Topical antifungals can be applied twice daily. Alternatively, one may stress keeping the feet dry by day and using the antifungal only at night. Topical agents include ketoconazole, miconazole, naftifine (Naftin), terbinafine, and tolnaftate.
In severe cases or cases requiring quick resolution, oral antifungals can be added to the regimen. Terbinafine is preferred over griseofulvin given the former’s greater affinity for keratinized skin and its fungicidal action against dermatophytes.
Maceration, severe erythema, or skin denudation suggests an accompanying bacterial infection. An antibiotic that covers gram-negative organisms as well as S. aureus is indicated.
Our patient had features of acute vesicular and interdigital tinea pedis (not an uncommon combination). He was started on terbinafine 250 mg once daily for 10 days as well as topical naftifine cream at night. Although he remained committed to wearing leather tennis shoes, he was willing to change his socks at least once daily and go barefoot at home. Having failed to respond quickly to topical antifungals previously, he understood that a longer trial of these agents was needed. However, his condition had virtually cleared at his two-week follow-up appointment.