What is the recommended treatment for a patient with a wart on the plantar aspect of the foot, considering their overall health and medical history, such as diabetes or compromised immune systems?

Treatment for Plantar Warts

First-Line Treatment Recommendation

For immunocompetent patients with plantar warts, initiate treatment with topical salicylic acid 50% (or 30% if 50% is not available) applied daily by the patient for up to 8 weeks, as this is equally effective as cryotherapy but more cost-effective and can be self-administered. 1, 2

Treatment Algorithm

Standard First-Line Approach

• Salicylic acid 50% (Verrugon) applied daily by the patient for up to 8 weeks provides a 14% complete clearance rate at 12 weeks, identical to cryotherapy, but costs significantly less (£101.17 less per patient) 1, 2
• The British Association of Dermatologists supports salicylic acid as a standard treatment option for plantar warts 3
• Application technique: Hydrate the skin for at least 5 minutes before application, apply thoroughly to the affected area, cover overnight, and wash off in the morning 4

Second-Line Treatment Options

If salicylic acid fails after 8 weeks or shows no substantial improvement after 3 applications:

• Cantharidin-podophyllin-salicylic acid (CPS) combination formulation applied by a healthcare provider every 2-3 weeks for up to 6 applications demonstrates high efficacy (95.8% complete clearance in one study, with 86.8% requiring only a single application) 5, 6
• This combination is particularly effective for recalcitrant plantar warts that have failed other treatments, including those caused by HPV biotype 27 5
• The British Association of Dermatologists reports clearance with 1-4 treatments over 16 weeks using cantharidin 0.7% 7

Alternative second-line option:

• Cryotherapy with liquid nitrogen delivered by a healthcare professional, up to 4 treatments spaced 2-3 weeks apart, provides equivalent efficacy to salicylic acid (14% clearance at 12 weeks) but is more expensive and requires provider administration 1, 2

Third-Line and Adjunctive Treatments

For resistant cases:

• Intralesional platelet-rich plasma (PRP) injection combined with topical salicylic acid 30% applied twice daily between monthly PRP sessions has shown complete clearance in resistant cases after 3 sessions 8
• Hyperthermia (localized heat up to 44°C for 30 minutes on 3 consecutive days) achieved 54% cure rate versus 12% with placebo in one randomized trial 3
• Photodynamic therapy (PDT) with aminolevulinic acid achieved 75% complete resolution in plantar warts, though hand warts respond better than plantar warts 3

Surgical Options (Last Resort)

• Curettage, cautery, or CO2 laser can be considered when conservative treatments fail, though high-quality evidence is lacking 3
• One case series reported 67% success with electrosection for solitary plantar warts, with higher relapse rates at weight-bearing sites 3

Critical Considerations for Special Populations

Diabetic Patients

• Do NOT confuse plantar warts with diabetic foot ulcers - the evidence provided includes extensive guidance on diabetic foot ulcers 3, 9, but these are entirely different conditions requiring different management
• For diabetic patients with actual plantar warts (not ulcers), use standard wart treatments but with heightened caution regarding skin integrity and infection risk
• Instruct diabetic patients never to walk barefoot, in socks only, or in thin slippers 3

Immunocompromised Patients

• Consider more aggressive treatment earlier in the course, as spontaneous resolution is less likely
• Monitor closely for treatment complications and secondary infections

Treatment Modification Guidelines

Change treatment modality if:

• No substantial improvement after 3 provider-administered treatments 7
• Salicylic acid shows no response after 8 weeks 1
• Cantharidin shows no response after 6 applications 7

Critical Safety Warnings

Cantharidin Use

• Cantharidin is highly toxic if taken systemically - apply carefully to avoid damaging surrounding skin, which can spread infection through autoinoculation 7
• The superficial acantholysis injury reduces scarring risk 7

Salicylic Acid Use

• Excessive repeated application will not increase therapeutic benefit but could result in increased local intolerance and systemic salicylism 4
• If excessive drying or irritation occurs, apply a bland cream or lotion 4
• Rinse hands thoroughly after application unless hands are being treated 4

Common Pitfalls to Avoid

• Do not use formaldehyde or glutaraldehyde as first-line treatments - these are allergenic and have only level 3 evidence 3
• Do not use monochloroacetic acid - it is highly toxic and corrosive 3
• Do not rely solely on surgical interventions without attempting conservative treatments first, as evidence for surgical approaches is limited 3
• Do not continue ineffective treatment beyond recommended timeframes - switch modalities if no improvement is seen 7

Patient Education Points

• Plantar warts have a 31-34% self-reported clearance rate at 6 months regardless of treatment type 1
• Treatment aims to accelerate resolution and reduce discomfort, not guarantee immediate cure
• Consistent daily application (for salicylic acid) or adherence to treatment schedule is essential for success
• Avoid walking barefoot in public areas to prevent spread and reinfection