What is the differential diagnosis of hyperkeratotic (thickened skin) lesions on the sole of the foot in an elderly female patient?

Differential Diagnosis of Hyperkeratotic Lesions on the Sole of the Foot in an Elderly Female

The differential diagnosis of hyperkeratotic lesions on the sole of the foot in an elderly female patient includes corns (heloma durum), calluses, plantar warts (verrucae plantares), porokeratosis, actinic keratoses, squamous cell carcinoma, focal palmoplantar keratoderma, and knuckle pads. 1

Primary Differential Diagnoses

Corns and Calluses (Most Common)

• Corns (heloma durum) present as hard, yellow lesions with a central nucleus or plug of keratin that extends downward in a cone-shaped point, causing pain described as "walking on a small stone or pebble" 2, 3
• Located typically on the tips of toes or underneath the metatarsal heads on weight-bearing surfaces 2
• Calluses appear as more diffuse thickened areas without a central core, generally less painful than corns 2
• Both enlarge with continuing friction as a direct hyperproliferative response of keratinocytes 2
• May appear red if inflamed 2

Seed Corns (Heloma Miliare)

• Frequently seen in elderly patients due to toe and foot deformity 2
• Multiple small hyperkeratotic lesions scattered across the sole 2

Plantar Warts (Verrucae Plantares)

• Hyperkeratotic lesions caused by human papillomavirus 4
• Distinguished from corns by the presence of black dots (thrombosed capillaries) when pared down
• Salicylic acid 6% is FDA-approved as adjunctive therapy for verrucae plantares 4

Neurovascular Hyperkeratosis (Rare but Important)

• A form of callus where nerve endings and blood vessels become prominent in the epidermis in response to trauma 2
• Presents as sensitive, painful areas that bleed with normal debridement 2
• Estimated to occur in <1% of patients, but very debilitating 2
• Usually affects skin overlying the calcaneum and hallux 2
• Results from long-standing gross hyperkeratosis 2

Secondary Differential Diagnoses (Require Biopsy)

Porokeratosis Ptychotropica

• Uncommon form presenting as symmetrical reddish to brown-colored hyperkeratotic, verrucous plaques 5
• Can occur on plantar surfaces with satellite lesions 5
• Critical consideration: Malignant change occurs in 7.5% of porokeratotic lesions, making early biopsy essential 5
• Histology shows characteristic cornoid lamellae 5

Actinic Keratoses

• Hyperkeratotic lesions on sun-exposed areas, though less common on soles 1
• Requires biopsy to distinguish from squamous cell carcinoma 1

Squamous Cell Carcinoma

• Must be excluded in any hyperkeratotic lesion that is atypical, non-responsive to treatment, or rapidly growing 1
• Biopsy is mandatory before aggressive debridement of suspicious lesions 2

Focal Palmoplantar Keratoderma

• Inherited or acquired disorder causing localized hyperkeratosis 1
• Distinguished by distribution pattern and family history

Critical Diagnostic Approach

Initial Assessment

• Examine for the central keratin plug: If present with cone-shaped extension, diagnosis is corn (heloma durum) 2, 3
• Assess pain pattern: Corns cause focal, sharp pain; calluses cause diffuse pressure discomfort 2
• Check for inflammation: Red appearance suggests inflamed corn or callus 2
• Palpate for tenderness: Neurovascular hyperkeratosis is extremely sensitive to touch 2

When to Biopsy

• Any atypical hyperkeratotic lesion not responding to standard treatment within 2-4 weeks 1
• Lesions with irregular borders, rapid growth, or bleeding 1
• Before intralesional steroid injection for resistant hyperkeratotic areas to exclude malignancy 2
• Suspected porokeratosis due to 7.5% malignant transformation risk 5

Special Considerations in Elderly Patients

• Screen for diabetes and peripheral neuropathy: These conditions require more cautious management and alter the differential 1
• Assess vascular status: Peripheral artery disease increases risk of complications from any intervention 6
• Evaluate footwear: Improper shoe gear is a major contributing factor in elderly patients 6
• Consider multiple contributing factors: Impaired vision, gait changes, past foot conditions, and neurovascular disease all contribute to hyperkeratotic disorders in the elderly 7

Common Pitfalls to Avoid

• Do not perform aggressive debridement without first ruling out neurovascular hyperkeratosis, as this causes severe pain and bleeding 2
• Never use chemical plasters for corn removal in elderly patients, especially those with diabetes 3, 8
• Avoid assuming all hyperkeratotic lesions are benign corns or calluses without proper examination for atypical features 1
• Do not overlook the possibility of malignancy in non-responsive or atypical lesions 5