DESCRIPTION

• Corns and calluses are pressure-generated hyperkeratotic skin conditions of the feet or hands.
• A callus (tyloma [Greek]) is a diffuse area of hyperkeratosis, usually without a distinct border. Typically, callus is the result of exposure to repetitive forces, including friction and mechanical pressure. They tend to occur on the palms of hands and soles of feet. Calluses may or may not be painful.
• A corn (heloma [Greek]) 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. Corns typically occur at pressure points, or result from poor fitting shoes or an underlying bone lesion/spur.
• 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
• Digital corns are also known as clavi or heloma durum.
• Intractable plantar keratosis (IPK) is a painful corn, 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 are the most prevalent of all foot disorders. Palmar calluses at metacarpal heads are also common.

ETIOLOGY AND PATHOPHYSIOLOGY

Common corns and calluses are skin signs and often produce symptoms, but are not a disease entity themselves. Repetitive, accumulated, or excessive friction and mechanical trauma on external skin produces a natural, protective dermal response of hyperkeratosis on hands and feet, particularly over bony prominences.

• Calluses typically form diffusely over bony prominences or deformities where there are repetitive forces and/or frequent weight-bearing forces. Examples include metatarsal head deformities or from ill-fitting shoes on normal bony anatomy. Although calluses may frequently form on palmar surfaces, symptoms are rare because these surfaces are nonweight bearing.
• Hard corns are an extreme form of callus with a keratin-based core, which in the case of IPK, may be derived from human papillomavirus (HPV), and extraordinary pressure. Corns are often found on the digital surfaces and commonly linked to bony protrusions, causing skin to rub against shoe surfaces. Corns rarely form on the hands (1).
• Soft corns arise from increased moisture from perspiration leading to skin maceration, along with mechanical irritation, especially between toes.

RISK FACTORS

• Extrinsic factors producing pressure, friction, moisture and local stress
  • Poorly fitting shoes with narrow toe box or with abrasive surfaces
  • Absence of socks or gloves for pressure mitigation or nonbreathable socks or gloves producing excess moisture
  • Repetitive activities: sports; guitar playing; manual labor; fingerstick testing; prolonged postures in prayer, gaming, or yoga
  • Walking barefoot or wearing thin-soled shoes offering no support
• Intrinsic factors
  • Bony malformations such as hammertoes, bunions
  • Neuropathy of distal extremities, such as frequently seen in diabetic patients
  • Gait disturbances

GENERAL PREVENTION

Reduce mechanical pressure or friction by wearing properly fitting shoes, gloves, and moisture wicking socks.Geriatric Considerations
Regular foot exams, more frequently for diabetic and/or peripheral vascular disease patients, to assess for skin integrity, neuropathy, and pressure points are paramount.

COMMONLY ASSOCIATED CONDITIONS

• Foot ulcers in vascularly compromised individuals due to history of smoking and poor circulation or secondary to diabetes with microangiopathy and neuropathy
• Cellulitis, focal or regional symptoms/signs:
  • Pain, increasing size, redness, pain, or swelling
  • Purulent discharge
  • Fever
  • Color changes: pale, red, black
  • Excessive heat or coolness of skin to touch