What is a plantar wart, its causes, symptoms, and treatment options?

Plantar Wart Overview

A plantar wart (Verruca plantaris) is a benign, hyperkeratotic lesion on the sole of the foot caused by human papillomavirus (HPV) infection of keratinocytes at the basal layer, resulting in epidermal thickening and hyperkeratinization. 1

Causative Agent

• HPV types 1,2,4,27, and 57 are the primary causative agents, with HPV-1 and HPV-2 being most common 2
• The virus infects keratinocytes at the basal epidermal layer, triggering abnormal proliferation 2

Transmission and Epidemiology

• HPV spreads through direct person-to-person contact or via contaminated environmental surfaces 1
• The virus may remain infectious outside the body for months or possibly years 1
• Infection is common in childhood but can occur at any age, affecting 5-30% of children and young adults 1
• Athletes are at increased risk due to shared facilities and equipment 1

Clinical Presentation

Appearance

• Thick, endophytic, hyperkeratotic papulonodules on the plantar surface of the foot 3
• Disrupted or absent skin lines across the lesion (distinguishing feature from corns/calluses) 4
• May appear as solitary lesions or mosaic patterns (multiple confluent warts) 1

Diagnostic Confirmation

• Paring down the wart with a scalpel reveals pinpoint bleeding as capillary loops of elongated dermal papillae are exposed 2, 4
• This "pinpoint bleeding" is pathognomonic and distinguishes plantar warts from corns (which show a translucent core) and calluses (which show homogenous keratin) 4
• Multiple "seeds" (thrombosed vessels) may be visible in the dermis after debridement 3

Symptoms

• Pain and discomfort, particularly with weight-bearing 5
• Often mistaken for calluses in athletes, leading to misdiagnosis 3

Natural History

Children

• 50% clear spontaneously within 1 year 1, 4
• Two-thirds clear by 2 years 1, 4
• Clearance typically begins with reduction in size followed by complete disappearance 1

Adults

• Much slower to clear, with persistence for 5-10 years not uncommon 1, 2
• Warts can persist for years with little or no inflammation 1

Treatment Options

First-Line Treatments

Salicylic Acid (Level of Evidence 1+, Strength A)

• 15-40% topical paints or ointments applied after paring down the wart 4
• Promotes exfoliation of infected epidermal cells 2
• Average cure rate of 13.6% for plantar warts (lower than for common warts on other sites) 6

Cryotherapy with Liquid Nitrogen

• Applied fortnightly for 3-4 months 4
• Average cure rate of 45.61% across studies 6
• More effective for hand warts than plantar warts 1

Alternative Treatments (Higher Cure Rates but Less Studied)

Cantharidin-Podophyllin-Salicylic Acid (CPA) Formulation

• Average cure rate of 97.82% 6
• Can cause intense inflammatory reaction with blistering and pain 1
• Requires careful application due to potential toxicity 1

Intralesional Bleomycin

• Average cure rate of 83.37% 6
• Requires injection technique 1

Intralesional Immunotherapy

• Average cure rate of 68.14% 6

Laser Therapy

• Average cure rate of 79.36% 6
• CO2 fractional laser combined with photodynamic therapy showed 90% clearance in periungual warts 1

Topical Antivirals

• Average cure rate of 72.45% 6
• Imiquimod 5% cream under occlusion with 40% salicylic acid pads has shown success 7

Other Modalities

Formaldehyde Soaks (Level of Evidence 3, Strength D)

• 3% soaks applied to pared plantar warts, with 80% cure rate in children 1
• Formaldehyde is allergenic 1

Glutaraldehyde 10% Paint (Level of Evidence 3, Strength D)

• 72% cure rate in resistant warts 1
• Risk of deep necrosis with repeated application, especially at concentrations >10% 1

Hyperthermia

• Localized heat (up to 44°C for 30 minutes on three consecutive days) showed 54% cure rate vs. 12% with placebo 1

Surgical Interventions (Level of Evidence 3, Strength D)

• Curettage, cautery, and CO2 laser are widely used but lack high-quality studies 1
• Relapse more common at weight-bearing sites 1

Treatment Algorithm

1. Expectant management is entirely acceptable for immunocompetent patients with asymptomatic warts, given high spontaneous clearance rates in children 4

2. For symptomatic plantar warts requiring treatment:

   • Start with salicylic acid 15-40% after paring down the lesion 4
   • If no response after 12 weeks, consider cryotherapy fortnightly for 3-4 months 4
   • For refractory cases, consider specialized treatments like CPA formulation, intralesional bleomycin, or immunotherapy 6

3. Avoid destructive treatments on facial warts due to scarring risk 4

Critical Pitfalls and Caveats

• All wart treatments have recurrence rates of at least 25% within 3 months because treatments do not eradicate HPV infection 4
• Never use chemical corn removers on diabetic patients due to high complication risk 4
• Avoid overdebridement, which can cause pain and tissue damage 4
• First-line treatments (cryotherapy and salicylic acid) have lower cure rates for plantar warts compared to warts on other body sites 6
• Treatment should be guided by anatomic site, size, number of warts, expense, efficacy, convenience, and potential adverse effects 4
• Persistent or extensive plantar warts in adults may warrant evaluation for underlying immune deficiency 2