Corns

A corn (clavus) is a small, well circumscribed, conical area of thickened stratum corneum, with a central core, produced by repeated focal pressure or friction over a bony prominence.

• Types:
  • Hard corn (heloma durum): dry, firm and painful, on the dorsum of the interphalangeal joints of the toes, or on the plantar surface under a metatarsal head.
  • Soft corn (heloma molle): macerated, rubbery and white, between the toes (usually the fourth web space), from the pressure of an adjacent bony prominence in a moist environment.
  • Seed corn (heloma miliare): small multiple corns in clusters on the sole.
  • Neurovascular corn: has a rich vascular and neural supply, so it is very painful.
• Causes: tight or ill fitting shoes, high heels, no socks, toe deformities (hammertoe, claw toe, mallet toe, bunion), prominent metatarsal heads, bony spurs, abnormal gait, flat or high arched feet, thin plantar fat pad and manual pressure on the hands (writers, musicians, tool workers).
• Corns are very common, with a prevalence of 14 to 48% depending on the population, more so in the elderly and in women.
• In diabetic and vascular patients, corns are ulcer precursors, because the pressure that thickens the skin also damages the tissue beneath it.

• A sharply demarcated, round or oval, yellowish, translucent or white thickened plaque, 2 to 10 mm, with a central polished core pointing inward. Pain occurs when pressure is applied directly (unlike a callus, which hurts less).
• Skin lines pass through and are preserved on the surface of the corn, and paring reveals a translucent core with no bleeding points.
• Soft corns macerate and may become infected, and may mimic a fissure or interdigital tinea.
• Bleeding under a corn (dark haemorrhage) or yellow serous fluid suggests tissue damage beneath and an impending ulcer.
• Differential diagnosis:
  • Plantar wart (verruca): interrupted skin lines, pinpoint black thrombosed capillaries after paring, pain on lateral squeezing.
  • Callus (diffuse, no core).
  • Porokeratosis (a ring with a thin raised ridge).
  • Foreign body granuloma.
  • Plantar keratoderma and punctate keratoses.
  • Squamous cell carcinoma and amelanotic melanoma (a lesion that is persistent, bleeds, or does not respond).
  • Gouty tophus, bursitis and rheumatoid nodule.
• Complications: pain, difficulty walking, bursitis, secondary infection and abscess, ulceration, osteomyelitis (in diabetic or neuropathic feet), and gait change causing secondary pain in the knee, hip and back.

• Clinical. Pare the lesion with a scalpel after soaking to confirm the translucent core and to separate it from a wart.
• Examine the whole foot and gait, footwear, bony deformities (flexible or rigid), and the range of motion at the toe and ankle joints.
• Check pulses, capillary refill, sensation (10 g monofilament, vibration) and for deformity in diabetic and elderly patients. Measure the ankle brachial pressure index if pulses are absent or reduced.
• X-ray if bony prominence, spur or osteomyelitis is suspected.
• Biopsy for any lesion that bleeds easily, grows, is pigmented, or does not respond to relief of pressure.

• Remove the pressure, as that is the cause and the corn will return otherwise:
  • Footwear with a wide, deep toe box and a heel under 3 cm, with soft uppers and adequate length, measured at the end of the day.
  • Cushioned insoles, silicone or felt padding, toe separators (for soft corns), and toe sleeves.
  • Donut or ring shaped pads over the corn to offload.
  • Custom orthoses for biomechanical abnormalities and prominent metatarsal heads.
  • Wear socks that are seamless and without tight elastic.
• Debridement: pare the corn with a sterile scalpel (number 10 or 15 blade) by a podiatrist or trained clinician, enucleating the core. Relief of pain is immediate. Repeat every 4 to 8 weeks as needed.
• Keratolytic therapy (in patients with normal sensation and good circulation):
  • Salicylic acid 15 to 40% plaster or collodion, applied to the corn only, kept for 24 to 48 hours then removed, followed by soaking and gentle rubbing with a pumice stone or emery board. Protect the surrounding skin with petroleum jelly or a ring pad. Repeat for up to 14 days.
  • Urea 20 to 40% cream applied nightly, and softened tissue pared.
  • Do not use salicylic acid plasters in diabetes, neuropathy, peripheral arterial disease, or frail skin. These patients should be treated by podiatrists only.
• Do not cut or shave corns at home. Avoid chemical corn removers in patients with diabetes, poor circulation or fragile skin.
• Infection: soft corns that become infected need cleansing, drainage of any abscess, and flucloxacillin 500 mg orally 6 hourly for 5 to 7 days (clindamycin 300 mg 8 hourly in penicillin allergy). Diabetic or neuropathic infection needs urgent specialist assessment with X-ray and broader antibiotic cover.
• Surgical correction for recurrent, painful corns over a fixed bony prominence, after failed conservative care:
  • Flexor tenotomy or tendon transfer for flexible hammertoe or claw toe.
  • Proximal interphalangeal joint arthroplasty or fusion for rigid hammertoe.
  • Condylectomy, exostectomy or metatarsal osteotomy for a plantar prominence.
  • Fat pad augmentation (injected filler) has limited evidence.
  • Surgery is avoided in patients with poor circulation until revascularisation.
• Special groups:
  • Diabetes and neuropathy: refer to a podiatrist or diabetic foot clinic, check feet daily, wear prescribed footwear, and treat blood under a corn as a pre-ulcer needing urgent review.
  • Peripheral arterial disease: debride cautiously by a specialist, and avoid sharp injury.
  • Anticoagulants and immunosuppression: paring needs care, and infection must be treated early.
  • Elderly: help with footwear, nail and foot care.
  • Children: corns are uncommon and suggest a structural abnormality or footwear problem, so refer for review.
• Follow up: review after 4 to 8 weeks for debridement and footwear adjustment. Refer to podiatry, orthotics, or orthopaedic surgery for recurrence, deformity or high risk feet, and to dermatology if the diagnosis is uncertain.