How should I manage a 45-year-old woman with painful plantar verrucae on the lateral left foot and heel causing gait disturbance and knee pain after unsuccessful over‑the‑counter salicylic acid, and what complications should I monitor?

Management of Refractory Plantar Verrucae

For this patient with painful plantar warts unresponsive to salicylic acid, cryotherapy with liquid nitrogen every 2 weeks for 3-4 months is the recommended second-line treatment, though you should counsel her that cure rates remain modest at approximately 30-39% for plantar warts. 1, 2

Why Salicylic Acid Failed and What This Means

• Plantar warts have inherently lower cure rates (14-33%) compared to warts at other body sites due to the thick plantar skin that prevents adequate treatment penetration 1, 2
• The expected cure rate for salicylic acid alone is approximately 33% for plantar warts, so treatment failure is common 1
• Critical question: Did she properly debride/pare the wart before each application? Failure to remove the thick keratin layer is the most common reason for treatment failure 1, 3

Second-Line Treatment: Cryotherapy

Initiate liquid nitrogen cryotherapy every 2 weeks for 3-4 months 1

• Expected cure rate is 30-39% with standard cryotherapy protocols 1, 2
• More aggressive cryotherapy regimens may achieve 65% efficacy but significantly increase pain, blistering, and scarring risk 1
• A recent 2025 multicentre RCT showed only 11% complete remission with cryotherapy as second-line treatment, highlighting the challenging nature of previously-treated plantar warts 4

Combination Therapy Option

Consider combining cryotherapy with continued salicylic acid application between treatments 1, 5

• One study reported 86% clearance with combined cryotherapy plus 70% salicylic acid, though this requires patient compliance 1
• A smaller study showed 89.2% eradication rate with combined cryotherapy and daily 70% salicylic acid application 5
• The patient must continue proper debridement before each salicylic acid application 1, 3

Third-Line Options for Resistant Cases

If cryotherapy fails after 3-4 months, consider:

• 5-Fluorouracil (5-FU) cream under occlusion: 95% clearance rate in adult plantar warts after 12 weeks, though a 2025 RCT showed only 3.5% complete remission as second-line treatment 1, 4
• Formaldehyde 3-4% solution: Daily 15-20 minute soaks 1
• Contact immunotherapy with diphenylcyclopropenone (DPC): 88% complete clearance with median treatment time of 5 months 1

Addressing the Secondary Complications

The knee pain from altered gait mechanics requires immediate attention:

• Refer to physiotherapy for gait assessment and knee rehabilitation 6
• Recommend cushioned footwear and protective padding over the heel wart to reduce pressure and improve weight distribution 7
• Consider temporary orthotic support to normalize gait pattern while treating the warts 6

Critical Caveats and What to Watch For

Before initiating cryotherapy, assess for contraindications:

• Avoid cryotherapy in patients with diabetes or impaired circulation 1
• Do not use near cutaneous nerves or tendons 1
• Warn about pain, blistering, and potential scarring with aggressive treatment 1

During treatment:

• Never damage surrounding normal skin during paring as this can spread HPV infection to adjacent areas 1, 3
• Monitor for treatment-related complications including infection (12% risk with some treatments) 6
• Patient compliance is often poor due to surrounding skin irritation and prolonged treatment courses 1

Set realistic expectations:

• Treatment duration must be adequate (3-4 months minimum) before declaring failure 1
• Spontaneous resolution occurs in approximately 30% of cases within 6 months, though this may not be acceptable given her functional impairment 1
• Plantar warts generally have lower cure rates than warts at other sites 1, 3

Surgical Options: Generally Not Recommended

Avoid surgical excision, curettage, or cautery as there are no high-quality studies supporting their use for plantar warts (Level 3 evidence, Strength D recommendation—the lowest possible rating) 6, 1

When to Refer to Podiatry

Consider referral if:

• Warts fail to respond to 6-8 weeks of topical keratolytic therapy 7
• Professional debridement is needed 7
• Underlying biomechanical issues require evaluation 7
• Orthotic intervention or specialized footwear modification is necessary 7