Description

• A callus (tyloma) is a diffuse area of hyperkeratosis, usually without a distinct border.
  • Typically, the result of exposure to repetitive forces, including friction and mechanical pressure; tend to occur on the palms of hands and soles of feet (1)
• A corn (heloma) is a circumscribed hyperkeratotic lesion with a central conical core of keratin that causes pain and inflammation. The conical core in a corn is a thickening of the stratum corneum.
• Hard corn or heloma durum (more common): often on toe surfaces, especially 5th toe (proximal interphalangeal [PIP]) joint
• Soft corn or heloma molle: commonly in the interdigital space (1)
• Digital corns are also known as clavi or heloma durum.
• Intractable plantar keratosis is usually located under a metatarsal head (1st and 5th most common), is typically more difficult to resolve, and often is resistant to usual conservative treatments.

Epidemiology

Corns and calluses have the largest prevalence of all foot disorders.

• Incidence of corns and calluses increases with age.
• Less common in pediatric patients
• Women affected more often than men
• Blacks report corns and calluses 30% more often than whites.

• 9.2 million Americans
• ~38/1,000 people affected

Etiology and Pathophysiology

Increased activity of keratinocytes in superficial layer of skin leads to hyperkeratosis. This is a normal response to excess friction, pressure, or stress.

• Calluses typically arise from repetitive friction, motion, or pressure to skin. The increased pressure is often secondary to a metatarsal deformity (long metatarsal or plantarflexed metatarsal) or another bone spur or deformity.
• Hard corns are an extreme form of callus with a keratin-based core. Often found on the digital surfaces and commonly linked to bony protrusions, causing skin to rub against shoe surfaces.
• Soft corns arise from increased moisture from perspiration leading to skin maceration, along with mechanical irritation, especially between toes.

Genetics
No true genetic basis was identified because most corns and calluses are due to mechanical stressors on the foot/hands.

Risk Factors

• Extrinsic factors producing pressure, friction, and local stress
  • Ill-fitting shoes or walking barefoot
  • Not using socks/gloves
  • Activities that increase stress applied to skin of hands or feet (manual labor, running, walking, sports)
• Intrinsic factors
  • Bony prominences: bunions, hammertoes, mallet deformities, deformed metatarsals
  • Motor or sensory neuropathy such as secondary to diabetes

General Prevention

External irritation and pressure are by far the most common cause of calluses and corns. General measures to reduce friction or pressure on the skin are recommended to reduce incidence of callus formation. Examples include wearing shoes that fit well and using socks and gloves.

Geriatric Considerations
In elderly patients, especially those with neurologic or vascular compromise, skin breakdown from calluses/corns may lead to increased risk of infection/ulceration. 30% of foot ulcers in the elderly arise from eroded hyperkeratosis. Regular foot exams are emphasized for these patients as well as diabetic patients (2).

Commonly Associated Conditions

• Foot ulcers: especially noted in diabetic patients or patients with neuropathy or vascular compromise
• Infection: look for warning signs including
  • Increasing size, redness, pain, or swelling
  • Purulent drainage
  • Fever
  • Change in color of fingers or toes
• Signs of gangrene (color change, coolness)