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): More often on toe surfaces, especially 5th toe (proximal interphalangeal [PIP]) joint
• Soft corn (heloma molle): Commonly in the interdigital space (1)
• Digital corns are also known as clavi.
• Intractable plantar keratosis is usually located under a metatarsal head (1st and 5th most common), is typically more difficult to resolve, and often resistant to usual conservative treatments.

Epidemiology

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

Incidence
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
• Nearly 38/1,000 people affected

Risk Factors

• Extrinsic factors producing pressure, friction, and local stress:
  • Ill-fitting shoes
  • Not using socks, gloves
  • Manual labor
  • Walking barefoot
  • Activities that increase stress applied to skin of hands or feet (running, walking, sports)
• Intrinsic factors:
  • Bony prominences: Bunions, hammertoes
• Enlarged bursa or abnormal foot function/structure: Hammertoe, claw toe, or mallet toe deformity

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

General Prevention

External irritation is by far the most common cause of calluses and corns. General measures to reduce friction 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).

Pathophysiology

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

Etiology

• Calluses typically arise from repetitive friction, motion, or pressure to skin.
• Soft corns arise from increased moisture from perspiration leading to skin maceration, along with mechanical irritation, especially between toes.
• 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.

Commonly Associated Conditions

• Foot ulcers, especially in diabetic patients or patients with neuropathy or vascular compromise
• Infection: Look for warning signs of:
  • Spreading or redness around sore
  • Puslike drainage
  • Increased pain/swelling
  • Fever
  • Change in color of fingers or toes
• Signs of gangrene