Clinical Overview

Warts (verruca vulgaris) are common benign skin growths caused by human papillomavirus (HPV) infection of epidermal cells. This prevalent condition affects 10% of general population, higher in children/immunocompromised. Over 100 HPV types exist; HPV-1, -2, -4, -27 cause common skin warts; HPV-1, -4 predominantly cause plantar warts. Multiple morphologic variants (common, plantar, flat, filiform) reflect different anatomic locations and viral types.

Epidemiology

Warts prevalence 10-20% in general population, 15-33% in children/adolescents. Peak incidence 12-16 years. Immunocompromised individuals (HIV CD4 <50, transplant) develop warts 10-15 fold higher. Plantar warts particularly common in: athletes (contact sports), immunocompromised, diabetes (impaired wound healing/immunity). Sexual transmission: genital warts (condyloma acuminata) caused by HPV-6, -11 (low-risk), -16, -18 (high-risk, malignancy potential). Spontaneous regression: 50% of warts resolve within 2 years (immune clearance); however, 40% persist or recur if inadequately treated. Recurrence rates post-removal: 10-50% depending on treatment modality and immunocompetence.

Pathophysiology

HPV enters epidermis through microtrauma, infecting basal keratinocytes via L1 capsid protein interaction with cellular receptors. Viral proteins E6/E7 inactivate p53 and retinoblastoma protein (Rb), disabling apoptotic checkpoints permitting uncontrolled keratinocyte proliferation. Wart formation results from: (1) hyperkeratosis and acanthosis (epidermal thickening), (2) papillomatosis (dermal-epidermal junction undulations), (3) parakeratosis (retention of nuclei in stratum corneum), (4) dilated capillaries creating black dots characteristic of plantar warts (thrombosed vessels). Host immunity critical: Th1-mediated response (CD4+ T cells recognizing HPV E2, E6, E7 antigens) establishes wart control; impaired immunity permits wart proliferation/persistence. Subclinical HPV infection exceeds clinical wart prevalence 10-fold, demonstrating latent viral burden.

Clinical Presentation

Common warts: 2-10mm dome-shaped papules with hyperkeratotic surface, often multiple. Distribution: hands (75%), feet, elbows, knees. Plantar warts: painful lesions on weight-bearing areas (heel, metatarsal head), appearing as endophytic nodule with hyperkeratosis and characteristic black dots (thrombosed capillaries). Flat warts: 1-4mm flat-topped papules, flesh-colored to tan, appearing on face/trunk. Filiform warts: pedunculated finger-like projections. Periungual warts: warts adjacent to nails, may disrupt nail growth. Genital warts (condyloma): flesh-colored verrucous papules/plaques on genitals, potentially malignant if high-risk HPV (16/18).

Diagnosis

Diagnosis primarily clinical based on characteristic hyperkeratotic papules with black dots (plantar). Dermoscopy reveals thrombosed vessels (punctate dots), acanthosis. HPV typing rarely needed for common warts (clinical diagnosis sufficient); reserved for genital/suspicious lesions (assess malignancy risk). Histopathology shows: hyperkeratosis, papillomatosis, parakeratosis, koilocytic changes (HPV-infected keratinocytes with perinuclear halos).

Treatment Algorithm

Observation: Spontaneous regression 30-50% within 2 years for immunocompetent. Reasonable approach for asymptomatic, non-traumatized warts; however, active treatment desired by most due to cosmetic concerns or discomfort.

Topical Keratolytic - First-Line: Salicylic acid 15-20% solution/ointment or 40% plaster applied daily. Mechanism: disrupts keratin cross-linking, removing wart tissue layer-by-layer. 70% clearance with consistent application x 12 weeks. Requires weekly trimming of loose hyperkeratotic tissue with pumice/file for efficacy. Alternative: lactic acid 12-17%, imiquimod 5% cream (immune stimulant inducing Th1 response).

Cryotherapy - Most Effective Topical: Liquid nitrogen (-196°C) applied 10-30 seconds per session, repeated every 2-4 weeks until resolution (typically 3-6 sessions). Efficacy 70-90% for common warts. Creates ice ball in wart and surrounding tissue, triggering inflammation and immune activation. Pain during thawing common. Blister formation expected (protective, aids resolution). Plantar warts require more aggressive freezing (30-60 seconds) x 6-10 sessions due to thick skin. Recurrence 10-20%.

Wart Removal - Moderate-Severe/Recalcitrant: Podofilox 0.5% solution (antimitotic agent) applied 3 times daily x 4 days, rest 3 days, repeat cycle x 4 weeks (topical, user-applied). Surgical removal: curettage (sharp removal with local anesthesia) followed by cauterization (electrical or laser) prevents recurrence. CO₂ laser ablation or erbium laser removes wart tissue layer-by-layer; effective but slower healing, potential scarring. Combination approach: cryotherapy initially, followed by curettage if incomplete response after 4-6 sessions.

Immunocompromised Patients: Aggressive treatment warranted (higher recurrence/persistence). Imiquimod 5% cream 3 times weekly shows 60% response (vs. 40% in immunocompetent). Combination topical salicylic acid + cryotherapy most effective. Oral antivirals (off-label): zinc supplementation 30mg daily, interferon alpha systemic injection 3 million units 3 times weekly (for extensive/refractory warts, 50% response). Immunocompetence restoration (CD4+ recovery in HIV on antiretrovirals) improves treatment response and spontaneous regression.

Prognosis

Warts: variable course with spontaneous regression 30-50% within 2 years. Treatment accelerates clearance: topical keratolytics/cryotherapy achieve 70-90% clearance within 3-6 months. Recurrence 10-30% post-treatment (depends on immune clearance of residual HPV). Scarring rare with cryotherapy/keratolytics; higher risk with aggressive surgical removal. Immunocompromised patients: slower response, higher recurrence (40-50%).

When to See a Dermatologist

Dermatologists confirm diagnosis, initiate treatment, and manage recalcitrant warts requiring cryotherapy/surgical removal. Refer genital warts for HPV typing (malignancy risk) and management.

Frequently Asked Questions

Q: Are warts contagious?
A: Minimally contagious. HPV can spread through direct contact or contaminated surfaces; however, most people exposed do not develop warts (host immunity determines). Risk highest with immunocompromised or traumatized skin. Avoid sharing towels/razors. Cover warts if possible.

Q: Will warts go away on their own?
A: 30-50% spontaneously regress within 2 years as immune system clears HPV. However, 50% persist or recur. Active treatment accelerates clearance to 3-6 months, avoiding prolonged infection/transmission risk.

Q: What's the best wart removal treatment?
A: Cryotherapy most effective (70-90% clearance). Salicylic acid slower but accessible/low-cost (70% clearance with adherence). Combination approach (cryotherapy + keratolytic) optimizes results. Multiple treatments usually required.

Q: Will warts leave scars?
A: Cryotherapy/keratolytics rarely scar. Surgical removal (curettage/laser) carries 5-10% scarring risk. Immunocompromised patients higher scarring risk from prolonged infection/inflammation.

References

  1. Gibbs S, et al. Local treatments for cutaneous warts. Cochrane Database Syst Rev. 2012;9:CD001781.
  2. Kwok CS, et al. Topical treatments for cutaneous warts. Cochrane Database Syst Rev. 2012;9:CD001781.
  3. Braun RP, et al. Dermoscopy of warts. Dermatol Clin. 2018;36(4):407-415.
  4. Sterling JC, et al. British Association Dermatologists' guidelines for management of cutaneous warts. Br J Dermatol. 2014;171(4):696-712.
  5. Stalkup ME, et al. Immunotherapy for cutaneous warts. Dermatol Clin. 2017;35(3):381-392.
  6. Salk RS, et al. Sodium nitrite, sodium thiosulfate treatment of verruca vulgaris. Arch Dermatol. 1987;123(8):1036-1039.
  7. Silverberg NB, et al. Cryotherapy for common warts. Dermatol Ther. 2013;26(2):87-93.
  8. Landry M, et al. Prevention and treatment of human papillomavirus-associated diseases. Am Fam Physician. 2016;93(5):354-362.
  9. Bruggink SC, et al. Cryotherapy for common cutaneous warts. Cochrane Database Syst Rev. 2010;12:CD001781.
  10. Colato C, et al. Common warts. Dermatol Ther. 2016;29(3):156-162.