Calluses

A callus (tyloma) is a diffuse, poorly demarcated area of thickened stratum corneum, without a central core, from repeated friction or pressure. It is a physiological protective response of keratinocytes to mechanical stress.

• Sites: the plantar forefoot under the metatarsal heads, the heel, the medial side of the great toe and the hallux, the fingers and palms (tool use, weightlifting, musical instruments, rowing), and over other pressure points (knuckles, knees, elbows).
• Causes: ill fitting footwear, high heels, going barefoot, bony deformities (bunion, hammertoe, plantar flexed metatarsal), a high arched or flat foot, abnormal gait, thin fat pad, obesity, occupational friction, and diabetic neuropathy.
• Heel calluses with fissures are associated with dry skin, obesity, open back footwear, diabetes, hypothyroidism and autonomic neuropathy.
• Extremely common, and benign in itself. Over a neuropathic foot, however, a callus is a major risk factor for ulceration.

• A flat or slightly raised, yellow grey, thickened plaque that is firm, hard, and wider than a corn, with indistinct borders. Skin lines are preserved. It is usually painless or only mildly tender, with pain on deep pressure.
• Fissures at the heel margins are painful and may bleed and become infected.
• In the neuropathic foot, a callus can bleed beneath the surface (a dark red or brown subcallus haemorrhage), a sign of tissue breakdown and an imminent ulcer.
• Differential diagnosis: plantar wart (interrupted skin lines, pinpoint bleeding), corn, hereditary or acquired plantar keratoderma, tinea pedis (moccasin type), psoriasis, eczema, porokeratosis, lichen simplex chronicus, arsenical keratosis, squamous cell carcinoma and acral melanoma.
• Complications: pain, fissures, infection, bleeding, ulceration, and gait alteration.

• Clinical, with paring (the absence of a central core and of pinpoint bleeding separates it from a corn or wart).
• Full foot examination: footwear, deformity, gait, joint mobility, pulses, capillary refill, skin integrity and sensation with 10 g monofilament and vibration testing. Measure the ankle brachial pressure index when pulses are weak or absent.
• Check HbA1c or fasting glucose, thyroid function and body mass index when appropriate.
• Dermoscopy and biopsy of any pigmented, ulcerated or non-responding lesion to exclude malignancy.

• Offload the pressure and correct the cause:
  • Well fitting, cushioned footwear with adequate depth and a firm sole, with an upper that does not rub.
  • Soft insoles, metatarsal pads or bars, and silicone or gel heel cups.
  • Custom orthoses for deformity, with rocker sole footwear when needed.
  • Avoid walking barefoot. Wear padded gloves for manual work.
• Soften and reduce the callus:
  • Soak the feet in warm water for 10 minutes, then rub gently with a pumice stone or foot file. Do this several times a week. Avoid aggressive filing.
  • Emollient with keratolytic: urea 10 to 25% cream (up to 40% for thick calluses) twice daily, which is the most useful approach, or salicylic acid 10 to 20% in an emollient base once or twice daily for limited areas.
  • Lactic acid 12% lotion twice daily for dry heels.
  • Nightly occlusion of the heel with urea cream under cotton socks speeds up softening.
• Professional debridement: scalpel paring by a podiatrist every 4 to 8 weeks, which gives immediate relief and lowers the plantar pressure.
• Heel fissures: apply urea 20 to 40% cream or salicylic acid 5 to 10% twice daily, with occlusion at night. Deep, painful fissures can be sealed with a skin adhesive (cyanoacrylate glue) or covered with a hydrocolloid dressing. Treat infection with flucloxacillin 500 mg orally 6 hourly for 5 to 7 days.
• Do not use salicylic acid plasters, acid solutions, blades or razors on the calluses in diabetes, neuropathy, arterial disease or skin fragility. Do not self-trim.
• Surgical correction for recurrent, painful calluses with fixed deformity: metatarsal osteotomy, hallux valgus correction, tendon lengthening, or hammertoe correction by an orthopaedic or podiatric surgeon, after failure of at least 3 months of conservative care.
• Special groups:
  • Diabetes and neuropathy: this is a high risk foot. Inspect the feet daily, use prescribed therapeutic footwear, have regular podiatry every 4 to 8 weeks, and treat subcallus haemorrhage as an urgent pre-ulcer needing offloading and specialist review within 24 to 48 hours.
  • Peripheral arterial disease: debride cautiously, and refer for vascular assessment where indicated.
  • Rheumatoid arthritis: forefoot deformity needs orthotic and footwear review.
  • Elderly: provide help with foot care, and examine feet at each visit.
  • Pregnancy: use emollients and urea, avoid salicylic acid over large areas, and provide supportive footwear.
  • Renal impairment: limit salicylic acid to small areas.
• Follow up: review every 4 to 8 weeks for debridement in high risk patients, and every 3 to 6 months otherwise. Refer to podiatry, orthotics or diabetic foot services, and to dermatology for keratoderma or suspected malignancy.