Skin Disorders of the Foot in Active Patients
Craig G. Burkhart, MD, MSPH
THE PHYSICIAN AND SPORTSMEDICINE - VOL 27 - NO. 2 - FEBRUARY 1999
In Brief: Skin disorders of the foot are common in patients who exercise. Knowing the causes, diagnostic indications, and treatment of seven common skin conditions—friction blisters, calluses, corns, talon noir, tennis toe, plantar warts, and tinea pedis—can help physicians manage these disorders in active patients.
Exercise and sports participation enhance physical and psychological well-being, but often involve wear and tear on the feet that can cause pedal aches and pains and injury. Skin disorders are among the most common sports-related foot problems. If managed improperly, conditions such as friction blisters or tinea pedis can impede regular exercise. Physicians who know how to assess and treat common cutaneous conditions of the feet can help minimize discomfort, speed recovery, and prevent recurrence so patients can continue to be active.
The skin is well adapted to a wide range of mechanical trauma. However, mechanical irritation such as sudden, intense friction or repetitive rubbing to which the skin has not adapted can cause cell necrosis within the epidermis, leading to a separation of the epidermal layers that fills with fluid—the classic friction blister.
Individuals whose feet are prone to friction blisters can minimize blister formation by keeping their feet as dry as possible. Helpful steps include the use of foot powders such as Zeasorb (Stiefel Laboratories, Inc, Oak Hill, New York), frequent changes of socks, wearing acrylic socks (1) or two pairs of socks (2), and wearing sandals or nonocclusive shoes when not exercising.
Another useful product is moleskin. Cut slightly larger than areas of intense friction or sensitive skin, it can help prevent blister formation. Liquid adhesives such as Mastisol (Ferndale Laboratories, Inc, Ferndale, Michigan) promote adherence of moleskin to the foot. Alternatives to moleskin are the "liquid" bandages such as New Skin (Medtech Laboratories, Inc, Jackson, Wyoming), which dries to form a tough protective covering on the skin.
Once a blister forms, it is sterile as long as it remains intact. Nevertheless, it is prudent to aspirate lesions that are more than 5 mm in circumference (3). Unroofing the blister is not recommended, since this increases discomfort and the risk of infection. Appropriate bandages, including an antibiotic ointment and either moleskin or gauze, should be applied over the roof of the intact blister.
Footwear should be examined to see if seams or rough areas correspond to the sites of blisters. Placing nonskid cushions or nonslip insoles in the shoe may prevent excessive foot movement during exercise (4).
Calluses are the skin's adaptation to frequent, low-intensity friction. They form through increased cell cohesion, reduced shedding, and a thickening of the outer epidermal layer of dead skin. The resulting indurated areas generally form over bony prominences and have accentuated normal skin lines throughout (figure 1). Calluses are usually not painful and, in fact, can benefit athletes, since the hardened skin protects areas subjected to repeated pressures.
If calluses become painful, treatment should reduce pressure and trauma to the foot. The first step is to make sure shoes fit properly. Shoe inserts that provide cushioning, such as gel insoles or Spenco Polysorb (Spenco Medical Corporation, Waco, Texas) reduce direct pressure to the metatarsals and heels of the feet, diminishing the development of calluses. Using full-sole inserts, however, may require patients to purchase shoes a half size larger than normal to make room for the insert.
Treatment can also include softening calluses with keratolytics such as a salicylic acid ointment or lotion (eg, Pansol [Baker Cummin Dermatological Pharmaceutical, Miami]) or a lactic-acid product (eg, Lac-hydrin [Westwood Pharmaceuticals, Inc, Buffalo]) (5). Another effective measure is to soak calluses in warm water and remove the softened keratin with an abrasive such as a pumice stone (6).
For most athletes, however, calluses are normal adaptations to external forces and need not be softened, padded, or scraped.
There are two types of corns: hard and soft. Hard corns, the more common variety, appear on the lateral surface of the toes and on the plantar surface of the foot overlying the distal metatarsal heads and are typically surrounded by callused skin (7). They are horny indurations and thickenings of the stratum corneum that form a conical, deep central core pointing toward the dermis. They are surrounded by semi-opaque thickening of the dead skin layer that is best seen after the surface keratin is pared (figure 2).
Soft corns are hyperkeratotic, sodden lesions that occur between the toes, usually between the fourth and fifth digits (figure 3). These corns are greyish-white and soft to palpation and have a slightly sour odor. They are caused by the overriding of adjacent phalanges or by the apposition of phalangeal condyles by narrow shoes.
Like calluses, corns form as a response to friction and pressure. Unlike calluses, corns have no papillary ridges, and the surface is burnished smooth because the skin responds to pinpoint pressure against a bony prominence by a rapid increase in cell production. This causes the development of layers of immature cells that never form a competent dead-skin layer as in a callus. Corns are tender on direct pressure.
Factors that contribute to corn formation include structural problems such as osteoarthritis, hammertoe, pes cavus, and hallux valgus. Corns on the dorsa of the toes and on the lateral side of the fifth toe are aggravated by tight-fitting shoes.
The treatment of most corns consists of decreasing the size of the hyperkeratotic growth and relieving or eliminating pressure on the affected area of the foot. Patients can reduce corn size by daily home treatment with over-the-counter preparations of 17% salicylic acid. Once or twice a week, the white, dead superficial tissue should be pared away with a pumice stone, nail file, or other debriding instrument. Patients should be carefully instructed to stop applying the keratolytic agent in the event of irritation or tenderness and to scrape away only nonsensitive tissue.
Paring corns in diabetic patients requires special care, since these patients often have no cutaneous pain in the foot as a result of peripheral vascular and neurologic changes. Debriding of corns in the elderly must also be done carefully to minimize the risk of infection. In both cases, corns should be pared gently after they have been soaked in water.
Pressure can be relieved by placing donut-shaped corn or gel-type pads, cotton balls, or lamb's wool over the corn. In addition, shoes should be sufficiently wide to prevent pinching of the toes or accentuation of pain. Other options include shoe padding or a leather metatarsal bar (6,8) that attaches to the outer sole of the shoe proximal to a painful plantar corn (9) or under the arch of the foot (6), thereby shifting the body weight off the lesion. As a general rule, however, accommodative orthoses or orthotic shoes work better than metatarsal bars.
Talon noir, or black heel, is an asymptomatic diffuse or speckled bluish-black patch that usually appears as a linear or irregular configuration on the back or side of the heel. It is typically seen in adolescents whose feet pound on hard surfaces in jumping sports such as basketball and volleyball (10).
The pigmentation is caused by extravasated blood in the upper dermis and epidermis from ruptured superficial capillaries. Shaving the superficial layer of the stratum corneum (figure 4) will demonstrate puncta of pigment and will help rule out plantar warts and acral lentiginous melanoma (6,11). No treatment is necessary besides reassurance, although the use of a felt heel, gel-type pad (4,12), or air- or gel-cushioned athletic shoes may eliminate the condition.
Tennis or Jogger's Toe
Subungual hematoma of the first and/or second toe is associated with activities such as tennis, squash, jogging, walking, hiking, mountain climbing, and skiing (4,6,13,14). It occurs when the foot slips and the toes repeatedly jam against the front of the shoe. The resulting hemorrhage can lead to onycholysis and loss of the nail. When swelling is sufficient, pain can be severe enough to limit activity.
In most cases, patients can continue to exercise if the injured toe has adequate room to dorsiflex, which may require cutting a slit in the shoe over the affected toe. In cases of extreme pain, using a heated paper clip or a CO2 laser, if available, to puncture the nail over a fresh hematoma instantly relieves the pain and may prevent avulsion of the nail. However, this procedure carries the risk of damaging the nail vascular matrix and is rarely necessary (4,6), since tennis toe usually heals on its own.
Prevention requires properly fitted shoes that allow some forward foot slippage without the jamming of toes—usually about 1/2 in. between the end of the longest toe and the end of the shoe. Keeping nails properly trimmed, tying laces tightly, and wearing shoes that have a side-to-side strap (4) to reduce forward movement of the foot during exercise can also be helpful.
Unlike the conditions described above, warts are caused by a human papillomavirus and not by physical activity. However, they can impair exercise performance if their location results in sufficient pressure to cause pain. Warts can also become infected, though their susceptibility to infection and the rate of resolution depend on the immune response of the host (15).
Plantar warts appear as sharply defined lesions that have a rough, hyperkeratotic surface surrounded by a smooth collar of thickened keratin. Gentle paring of the superficial dead skin layer over the wart allows better differentiation between wart tissue and the surrounding skin lines (figure 5). A wart can be distinguished from normal skin by its soft keratinous mass and hypertrophied papillae with punctate black dots representing thrombosed capillaries. Further paring causes pinpoint bleeding from these capillaries. Such findings easily differentiate warts from plantar keratoses and corns.
Most plantar warts are found at pressure points on the heel or over the metatarsal heads (16). Although most patients have one or two warts, some have clusters (figure 6) that are called mosaic warts. Warts can be asymptomatic but can also cause disabling pain. The larger the wart and the closer it is to a pressure point like a metatarsal head, the greater the likelihood of pain or discomfort.
No vaccine is yet available, so treatment usually involves some form of destruction; the modalities include chemicals, surgery, lasers, cryosurgery, cytotoxins, and interferon injections. In choosing a treatment, physicians and patients should weigh the degree of the patient's disability and discomfort with the possible side effects of treatment and the possibility that the warts will spontaneously resolve.
In our clinic, we instruct patients on the daily use of over-the-counter 17% salicylic acid keratolytics and weekly paring. The persistent irritation from these agents may stimulate the patient's immune system to increase activity in the area of the warts, and they also soften the lesion. Each month the physician pares the lesion with a scalpel to reduce its bulk and applies liquid nitrogen, the preferred modality because of its low propensity for scarring (17).
With recalcitrant warts, surgery with simple curettage to the base of the lesion is possible. However, surgery can cause scarring, and recurrence at the surgery site is not uncommon. Treatments with immune modulators such as cytotoxins and interferon injections have been only marginally successful because of the inaccessibility of the wart virus within the nucleus of the host's epidermal cells.
Fungal infections of the feet are common among athletes and in the general population. Tinea pedis is rare in children under 10 but occurs frequently in adolescents and in males more than females.
Tinea pedis has three clinical forms. Intertriginous involvement of the toe webs is the most common (figure 7). This type appears as a scaly, peeling eruption, with or without erythema, that may develop white maceration and soggy scaliness with fissuring. A second form is the moccasin distribution (figure 8), which affects the entire plantar surface with hyperkeratotic scaling and minimal erythema. The last variant is an acutely inflammatory eruption, with vesicles and bullae, usually located on the midsole of the foot.
The fungi that cause tinea pedis, found in high levels on swimming pool decks and in locker rooms, are ubiquitous. The body's natural immune system allows them to inhabit the skin without infection. However, people have varying degrees of natural immunity to the organisms, and moisture can create an environment conducive to fungal invasion.
An essential element of prevention and treatment of fungal infection is keeping the feet dry. Patients should dry between the toes after a shower, apply foot powder daily, change socks if they become moist, wear nonocclusive shoes, and go barefoot when possible.
Treatment also includes the application of antifungal cream in the evenings. The allylamines (terbinafine, naftifine) are slightly superior to the imidazoles (miconazole, econazole, clotrimazole) but are more expensive. However, any of these medications will be effective in most cases. They may be applied a second time during the day, but keeping feet dry with powder usually yields better results.
In stubborn or severe cases, patients should take a 10-day course of oral terbinafine (a 250- mg tablet daily), itraconazole (two 100-mg tablets daily), or griseofulvin (250 mg daily), while continuing to use an antifungal cream.
Prevention and Intervention
Educating our active patients about pedal skin problems is important because many of these conditions can be prevented or minimized. However, when hygienic steps such as keeping the feet dry, wearing properly fitted shoes, and paring calluses or corns are inadequate, physicians need to step in with other measures to limit the effects of these disorders so that patients can remain active.
Dr Burkhart is a clinical assistant professor in the department of medicine at the Medical College of Ohio in Toledo and at Ohio University College of Osteopathic Medicine in Athens, Ohio. Address correspondence to Craig G. Burkhart, MD, MSPH, 5600 Monroe St, Suite 106 B, Sylvania, Ohio 43560.