Calluses and corns are caused by intermittent pressure or friction, usually over a bony prominence (eg, calcaneus, metatarsal heads).
Corns consist of a sharply circumscribed keratinous plug, pea-sized or slightly larger, which extends through most of the underlying dermis. An underlying adventitial bursitis may develop. Hard corns occur over prominent bony protuberances, especially on the toes and plantar surface. Soft corns occur between the toes. Most corns result from poorly fitting footwear, but small seed-sized corns on non–weight-bearing aspects of the soles and palms may represent inherited keratosis punctata.
Calluses lack a central plug and have a more even appearance. They usually occur on the hands or feet but may occur elsewhere, especially in a person whose occupation entails repeated trauma to a particular area (eg, the mandible and clavicle of a violinist).
Calluses are usually asymptomatic but, if friction is extreme, may become thick and irritated, causing mild burning discomfort. At times, the discomfort of calluses near the toes may mimic that of interdigital neuralgia.
Corns may be painful or tender when pressure is applied. A bursa or fluid-filled pocket sometimes forms beneath a corn.
A corn may be differentiated from a plantar wart or callus by paring away the thickened skin. After paring, a callus shows smooth translucent skin, whereas a wart appears sharply circumscribed, sometimes with soft macerated tissue or with central black dots (bleeding points) representing thrombosed capillaries. A corn, when pared, shows a sharply outlined yellowish to tan translucent core that interrupts the normal architecture of the papillary dermis.
Keratolytics (eg, 17% salicylic acid in collodion, 40% salicylic acid plasters, 40% urea) can also be used, taking care to avoid applying the agents to normal skin. Normal skin may be protected by covering it with petrolatum before application of the keratolytic.
Cushioning and altering foot biomechanics can help prevent corns and help treat existing corns. Although difficult to eliminate, pressure on the affected surface should be reduced and redistributed. For foot lesions, soft, well-fitting shoes are important; they should have a roomy toe box so that toes can move freely in the shoe. Stylish shoes often prevent this freedom of motion. Shoes that increase discomfort of a lesion should be eliminated from the wardrobe. Pads or rings of suitable shapes and sizes, moleskin or foam-rubber protective bandages, arch inserts (orthotics), or metatarsal plates or bars may help redistribute the pressure. For corns and calluses on the ball of the foot, an orthotic should not be full length but should extend only to the ball or part of the shoe immediately behind the corn or callus. Surgical off-loading or removal of the offending bone is rarely necessary.
Patients who have a tendency to develop recalcitrant painful calluses and corns may need regular care from a podiatrist. Patients who also have impaired peripheral circulation, particularly if they also have diabetes, require intensive foot care.
The cause of corns and calluses is usually intermittent pressure or friction, usually over a bony prominence.
After paring away the thickened overlying skin, a wart will bleed, whereas a corn will not.
Recommend mechanical abrasion and keratolytics to help remove corns and calluses.
Recommend cushioning and redistributing pressure in the foot to help prevent corns and calluses.
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