Skin Disorders Guide

Eczematous dermatitis disease of the feet may be caused by anyone of the following six processes: dyshidrotic eczema, atopic dermatitis, vesicular tinea pedis, allergic contact dermatitis, irritant contact dermatitis, and stasis dermatitis. The problems in differential diagnosis are quite similar to hand eczema, but recognition is further hampered by the confounding effect of shoes and stockings.

Dyshidrotic eczema of the foot is distinguished from the other eczematous diseases in that the process begins as dyshidrosis. Patient history identifies the fact that minute, noninflammatory vesicles preceded the appearance of the eczematous changes. These changes begin on the tips and sides of the toes; the clinical characteristics are otherwise similar to those described for dyshidrotic eczema of the hands. Dyshidrotic eczema of the feet is a particularly common problem in children.

Atopic dermatitis of the foot is distinguished by the fact that itching precedes any evidence of skin disease. Moreover, the distribution pattern, which involves the dorsal surface of the distal foot, is highly characteristic. Lesions may also occur around the ankle near the malleoli. The plaques of atopic dermatitis on the foot are often quite sharply marginated and are often nummular in size and shape. In some instances, however, autoeczematization causes the disease to cover the entire foot. The itch-scratch cycle is prominent. Excoriations and lichenification are regularly present

Tinea pedis is an extraordinarily common condition, but it is less often the cause of foot eczema than one might expect. Those patients who do develop foot eczema as a result of tinea pedis are rather likely to have a history of preceding, chronic fissuring of the lateral toe webs. On examination, multilocular vesicles and bullae of the instep are regularly found. The dorsal surface of the foot becomes involved late in the course of the disease through the process of autoeczematization. Foot eczema secondary to fungal disease rarely, if ever, occurs prior to puberty. The typical distribution and course, together with the presence of onychomycosis and positive potassium hydroxide (KOH) preparations, allow for definitive identification.

Allergic contact dermatitis occurs primarily on the dorsal surface of the toes. Consequently, it is easily confused with atopic dermatitis. In contrast to atopic dermatitis, however, a rash is present at the time pruritus is first noted. Also, lichenification is not usually present. Most allergic contact dermatitis of the foot is due to the products used in the manufacture of shoes. These include glues, chemicals used in rubber processing, and chromates used in leather tanning. A suspected diagnosis can be confirmed by patch testing. Such tests are most practically carried out by removal of a small piece of the inner portion of the shoe. This material can then be bandaged directly to the patient’s skin in the manner described . Patch testing can also, of course, be carried out with chemicals supplied in most patch testing kits. Contrary to widespread belief, allergic contact dermatitis is not a common cause of foot eczema.

Irritant contact dennatitis of the foot has a distinctive appearance. The plantar and dorsal surfaces of the toes are dull red and shiny. Examination reveals chapping with hundreds of minute cracks and fissures. Peeling of the tips and plantar surface of the toes is usually present. The problem presumably starts because of maceration secondary to sweat retention. This condition is particularly likely to occur in individuals with hyperhidrosis of the feet and in those who wear shoes that retard evaporative loss of moisture. Consequently, it is an extraordinarily common problem in children who wear rubber-soled, tennis-type shoes all day long.

Stasis dennatitis of the foot occurs in older adults who have a history of chronic ankle swelling. The eruption begins first at the ankle and only subsequently extends to the rest of the foot. Appreciable swelling of the foot and ankle is always present. The dorsal aspect becomes involved first, but plantar disease is present in persistent, severe cases. Pigmentary changes secondary to both heme and melanin pigments are usually noted.

Foot eczemas, like hand eczemas, are commonly complicated by the development of autoeczematization. This process results in local as well as distant spread of eczematous disease outside of the original distribution pattern. The presence of alltoeczematization greatly hampers recognition of the originating eczematous process. Recognition of the various foot eczemas is also hindered by the regular presence of irritant contact dermatitis secondary to the retention of serum and sweat underneath footwear. Because of these two factors, it is often necessary to use a short course of systemic steroids so that the initial changes can be identified as they occur.