Clinical Dermatology

Diagnostic Hallmarks

1. Distribution: plantar aspect, especially instep, of the foot
2. Associated fungal infection of the toenails and web space
3. Positive potassium hydroxide (KOH) preparation from vesicle roof

Clinical Presentation

Fungal infections can occur anywhere on the body, but blister formation as a component of fungal infection occurs only on the plantar surfaces of the feet. The vesicles of tinea pedis are usually confined to the instep, but they are accompanied by red scaling lesions on the remainder of the plantar surface and by lateral web space cracking and fissuring. Onychomycosis is also often present. The vesicles of tinea pedis are 5-10 mm in diameter and they are usually clustered tightly, sometimes to the point where they form a large, multilocular bulla. Relatively little inflammatory change is found around the base of the blisters. The fluid contained in the vesicles is usually somewhat cloudy. Severe vesicular fungal infections of the feet are sometimes accompanied by a sterile vesicular or eczematous eruption on the hands. This process of autosensitization is known as the dermatophytid or “id” reaction.

A clinical diagnosis of vesicular tinea pedis should be supported by objective evidence of fungal infection. This is most easily carried out via a KOH preparation. A small pointed scissors is used to trim away a vesicle roof. The roof is then placed on a microscope slide and is covered with several drops of 10-20% KOH solution. The preparation is set aside for approximately 20-30 minutes in order for the roof to dissolve sufficiently for fungi to be visualized. Alternately, the roof can be sent for fungal culture, but this results in a delay of 2 weeks before confirmation is available.

Course and Prognosis

Tinea pedis rarely occurs in children, but it is a rather common problem in teenagers and adults. Men are affected several times more frequently than are women. The infection, once present, is chronic with intermittent periods of exacerbation and remission. Trauma to the feet accompanied by heat and sweating will activate a previously quiescent infection. Individual episodes of vesicular tinea pedis, unless treated, can progress to chronic foot eczema .

Pathognesis

Vesicular tinea pedis is caused by the dermatophyte fungal organisms, Trichophyton rubrum, Tmentobtophytes, and Epider­mophyton floccosum. A surprisingly large proportion of the human population carries Trichophyton sp. on its feet, and this in turn leads to high contamination levels on floors. Most contagion appears to occur because of barefoot contact with such contaminated floors, but to a limited degree, person-to-person contagion might be possible. Simple contact with the fungal organisms is not sufficient to cause infection. Broken skin and a warm moist environment must also be present. Thus, it is no wonder that the sweaty, traumatized feet of physically active people are so often infected. Atopics and other people with defective cell-mediated immune responsiveness are particularly subject to infection. Once present, the organisms live indefinitely in the thick dead layers of the stratum corneum. For the most part, this is a symbiotic relationship with little host response until the equilibrium is disturbed. At that point, fungal proliferation develops and an inflammatory response is triggered.

Therapy

Topical antifungal agents are not always effective in the treatment of vesicular tinea pedis. Griseofulvin or, possibly, ketoconazole can be given for a period of about 3 weeks. This usually results in resolution of visible disease, but total eradication of organisms is generally not possible no matter how long the antifungal agent is used. Long-term topical antifungal therapy should be substituted, once the patient is asymptomatic, in order to minimize fungal proliferation. Environmental factors also ought to be optimized. The feet should be kept as cool and dry as possible. Leather soled shoes and cotton blend socks are of help. Tennis-type shoes, because of their nonporous rubber soles, should be avoided except for use during a specific athletic event.

This entry was posted on Wednesday, August 22nd, 2007 at 4:15 am and is filed under Vesiculobullous Diseases. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.