Viral warts are common and caused by HPV. Verrucas are very common in children. They are spread by contact of bare feet with the virus, and are more troublesome in immunosuppressed patients.
Clusters of warts may spread across the sole of the foot, known as mosaic warts. These are not usually painful but may be more difficult to clear. In 50 per cent of cases, warts disappear spontaneously within six months and 90 per cent will clear after two years. Treatments are occlusion, topical salicylic acid, 3% formalin soaks or cryotherapy.
Pitted keratolysis is a problem of 'smelly feet' caused by corynebacteria. It usually occurs in patients with sweaty feet, especially if they wear occlusive footwear. On close inspection symmetrical, small, punched out erosions can be seen over the weight-bearing areas of the feet. The instep is usually spared. The patient should be advised to wear 'open' shoes, to apply an antiperspirant to the feet and to wash with soap or an antibacterial cleanser. Rapid improvement should follow the application of topical fusidic acid or mupirocin or, if necessary a course of oral erythromycin or clindamycin.
Plantar pustular psoriasis
Patients develop crops of sterile pustules on one or both feet. The skin may also be thickened, red and scaly, and painful cracks and fissures may develop. Some, but not all, patients may be known to suffer with psoriasis. It appears to be much more common in smokers or ex-smokers. This condition may persist for years and tends to be poorly responsive. Treatments include coal tar and salicylic acid, dithranol or a potent topical steroid such as betamethasone, and emollients. It may be necessary to try acitretin, PUVA or a cytotoxic drug such as methotrexate, azathioprine or hydroxyurea.
Tinea pedis is due to a dermatophyte fungal infection, Trichophyton rubrum, T interdigitale, or Epidermophyton floccosum. It commonly causes moist, peeling areas between the toes and/or blisters or pustules over the instep or sides of the feet. Diagnosis may be confirmed by microscopy or skin scrapings. Topical application of an imidazole cream twice daily or terbinafine cream once daily for two weeks should clear the problem. For non-responsive, persistent problems oral terbinafine for two weeks or griseofulvin for six weeks may be required.
Corns and calluses
Corns and calluses commonly occur on the soles of the feet as the result of pressure and friction. Repeated trauma to the area causes a localised hyperkeratosis with a central core over bony prominences. Direct pressure on a corn is painful. After paring, it looks more normal whereas small bleeding points will be displayed after paring a verruca. The patient should be advised on footwear and some will gain relief by the application of 5-10% salicylic acid, nightly, to soften the keratin. Corn pads or foam insoles may also be helpful. A chiropodist can pare the corn and provide useful advice.
Keratoderma is a problem in which patients suffer from gross thickening of the skin of the soles of the feet. The keratoderma may be diffuse, focal or punctuate, with numbers of small hyperkeratotic papules. Some cases are genetically determined by an autosomal dominant or autosomal recessive gene. Others may be associated with conditions such as psoriasis, eczema, SLE, lymphoedema, medications such as lithium or chemotherapeutic agents. Treatment aims to soften the skin with emollients, keratolytics, topical retinoids or calcipotriol or systemic retinoids.