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Chapter 36: Skin Diseases of the Feet

Noah Goldfarb; Steven W. Lin

INTRODUCTION TO CHAPTER

The plantar surface of the foot has the thickest keratin layer, a high concentration of eccrine sweat glands, as well as sensory nerves, including Pacinian corpuscles, and other mechanoreceptors. The combination of abundant keratin and sweat creates an ideal environment for fungal infections. Friction and contact with footwear also make the feet susceptible to contact dermatitis. In addition, the feet are disproportionally affected by vascular disorders, due to their gravity-dependent anatomical location, and by peripheral small fiber sensory neuropathies. Since the feet are a site of frequent injury, vascular disorders and sensory neuropathies predispose this area to recurrent and difficult-to-manage wounds.

APPROACH TO DIAGNOSIS

The most common causes of skin diseases on the feet are dermatophyte infections and inflammatory dermatoses (see Table 36-1). Clinically these two categories of disease are often indistinguishable from one another. The presence of fissures and/or scale in the toe web space and nail dystrophy is more suggestive of a dermatophyte infection, but nail dystrophy can also occur in psoriasis.

Table 36-1.Differential diagnosis for diseases of the feet.
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Table 36-1. Differential diagnosis for diseases of the feet.
Disease Epidemiology History Physical Examination
Inflammatory
Allergic contact dermatitis

Common

F > M

Age: any age

Pruritus and painful fissures

Onset: hours to days after contact with allergen

Acute: Papules and vesicles on an erythematous base (Figures 8-4 and 8-5)

Chronic: xerosis, fissuring, hyperpigmentation, and lichenification (Figures 8-1, 8-2, 8-3)
Atopic dermatitis

Common

M ≥ F

Age: usually begins in childhood but may persist

Pruritic and painful

Chronic waxing and waning course

Family history of atopy

 Presents with swelling, xerosis, fissuring, erythema, and lichenification on the dorsal feet and soles (Figure 2-10)
Dyshidrotic dermatitis

Common

F ≥ M

Age: usually young adults

 Severely pruritic or painful. Chronic and recurrent with episodes lasting 2-3 weeks Multiple grouped vesicles and erosions on a noninflammatory base located on the soles (Figure 8-12)
Psoriasis vulgaris

Common

M = F

Age of onset: any age, but peaks in 20s and 50s

Pruritic and painful

Chronic, indolent course. Associated with arthritis and nail pitting/dystrophy

Family history of psoriasis

 Well-demarcated plaques with adherent, thick scale on an erythematous base. Less commonly present with pustules over pressure-bearing regions of the soles (Figure 9-1)
Palmoplantar pustulosis

Uncommon

F > M

Age: 50-60 years of age

Pruritus, burning or pain

Chronic waxing and waning course

 Scattered creamy-yellow pustules and dusky-red macules on soles, with a tendency to affect the heel and instep of the foot; may be bilateral or unilateral
Infectious
Tinea pedis

Common

M > F

Age: post-puberty

Asymptomatic or pruritic

Lasts months to years

Associated with onychomycosis

Interdigital type: dry scaling and/or maceration, peeling, and fissuring in toe webs (Figure 10-9)

Moccasin type: well-demarcated erythematous patch with fine, white ...

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