Chapter 134. Plantar Warts

A 15-year-old boy presents with painful growths on his right heel for approximately 6 months (Figure 134-1). It is painful to walk on and he would like it treated. He was diagnosed with multiple large plantar warts called mosaic warts. The lesions were treated with gentle paring with a #15 blade scalpel and liquid nitrogen therapy over a number of sessions. He and his mom were instructed on how to use salicylic acid plasters on the remaining warts.

Plantar warts (verruca plantaris) are human papilloma virus (HPV) lesions that occur on the soles of the feet (Figures 134-1, 134-2, 134-3, 134-4, and 134-5) and palms of the hands (Figure 134-6).

Palmoplantar warts, myrmecia.

• Plantar warts affect mostly adolescents and young adults, affecting up to 10% of people in these age groups.1
• Prevalence studies demonstrate a wide range of values, from 0.84% in the United States2 to 3.3% to 4.7% in the United Kingdom,3 to 24% in 16- to 18-year-olds in Australia.4

• Plantar warts are caused by HPV.
• They usually occur at points of maximum pressure, such as on the heels (Figures 134-1, 134-2, 134-3, and 134-4) or over the heads of the metatarsal bones (Figure 134-5), but may appear anywhere on the plantar surface including the tips of the fingers (Figure 134-7).
• A thick, painful callus forms in response to the pressure that is induced as the size of the lesion increases. Even a minor wart can cause a lot of pain.
• A cluster of many warts that appear to fuse is referred to as a mosaic wart (Figures 134-1 and 134-4).

• Young age.
• Decreased immunity.

Clinical Features

Plantar warts present as thick, painful endophytic plaques located on the soles and/or palms. Warts have the following features:

• Begin as small shiny papules.
• Lack skin lines crossing their surface (Figure 134-3).
• Have a highly organized mosaic pattern on the surface when examined with a hand lens.
• Have a rough keratotic surface surrounded by a smooth collar of callused skin
• Painful when compressed laterally.
• May have centrally located black dots (thrombosed vessels) that may bleed with paring (Figures 134-1, 134-2, 134-3, 134-4, and 134-5, Figure 134-6, and 134-7).

Typical Distribution

• They occur on the palms of the hands and soles of the feet. They are more commonly found on weight-bearing areas, such as under the metatarsal heads or on the heel.5

Biopsy

• If the diagnosis is doubtful, a shave biopsy is indicated to confirm the diagnosis.6

• Corns and calluses are pressure-induced skin thickenings that occur on the feet and can be mistaken for plantar warts. Calluses are generally found on the sole and corns are usually found on the toes. Calluses and corns have skin lines crossing the surface, and are painless with lateral pressure (see Chapter 207, Corn and Callus).
• Black heel presents as a cluster of blue-black dots that result from ruptured capillaries. They appear on the plantar surface of the heel following the shearing trauma of sports that involve sudden stops or position changes. Examination reveals normal skin lines, and paring does not cause additional bleeding. The condition resolves spontaneously in a few weeks.
• Black warts are plantar warts undergoing spontaneous resolution, which may turn black and feel soft when pared with a blade.7
• Squamous cell carcinoma should be considered when lesions have irregular growth or pigmentation, ulceration, or resist therapy, particularly in immunosuppressed patients (see Chapter 171, Squamous Cell Carcinoma).
• Amelanotic melanoma, although extremely rare, can look similar to HPV lesions. Lesions that are treatment resistant or atypical, particularly on the palms or soles, should be monitored closely. A biopsy is required to establish the diagnosis (see Chapter 172, Melanoma).
• Palmoplantar keratoderma describes a rare heterogeneous group of disorders characterized by thickening of the palms and the soles that can also be an associated feature of different syndromes. They can be classified as having uniform involvement versus focal hyperkeratosis located mainly on pressure points and sites of recurrent friction (Figure 134-8). This latter type can be differentiated from plantar warts by the more diffuse locations on the palmoplantar surfaces, the mainly epidermal involvement, and biopsy, if necessary (Figure 134-9).

Nonpharmacologic

• Painless plantar warts do not require therapy. Minimal discomfort can be relieved by periodically removing the hyperkeratosis with a blade or pumice stone.
• Painful warts should be treated using a technique that causes minimal scarring as scars on the soles of the feet are usually permanent and painful.
• Patients with diabetes must be treated with the utmost care to minimize complications.

Medications

• Topical salicylic acid solutions are available in nonprescription form and provide conservative keratolytic therapy. These preparations are nonscarring, minimally painful, and relatively effective, but require persistent application of medication once each day for weeks to months. The wart is first pared with a blade, pumice stone, or emery board, and the area soaked in warm water. The solution is then applied, allowed to dry, reapplied, and occluded with adhesive tape.8 White, pliable, keratin forms and should be pared away carefully until pink skin is exposed.9 SOR B
• Seventeen percent to 50% salicylic acid solution and plasters are available in nonprescription and prescription forms. However, the 17% solutions are more prevalent and easier to find in nonprescription form. The treatment is similar to the previous process, except that with plasters the salicylic acid has been incorporated into a pad. They are particularly useful in treating mosaic warts covering a large area. Pain is quickly relieved in plantar warts, because a large amount of keratin is removed during the first few days of treatment.9 SOR B A recent multicenter, open-label, randomized, controlled trial found that 50% salicylic acid and the cryotherapy were equally effective for clearance of plantar warts.10 SOR A
• Acid chemotherapy with trichloroacetic acid (TCA) or bichloracetic acid (BCA) is commonly employed to treat plantar warts in the office. They are considered safe during pregnancy for external lesions. The excess keratin is first pared with a scalpel, then the entire lesion is coated with acid, and the acid is worked into the wart with a sharp toothpick. The process is repeated every 7 to 10 days. SOR C
• Cryotherapy with liquid nitrogen therapy is commonly used, but plantar warts are more resistant than other HPV lesions. The liquid nitrogen is applied to form a freeze ball that covers the lesion and 2 mm of surrounding normal tissue, usually 10 to 20 seconds per freeze. SOR C There is no evidence that two freezing episodes are better than one, other than it allows for more freeze time in a way that is more acceptable to the patient. It is always better to underfreeze than to overfreeze in areas where scarring can produce permanent disability.
• Treatments for resistant lesions are often carried out in referral practices that have a high enough volume to use more expensive or specialized therapy. Cantharidin is an extract of the blister beetle that is applied to the wart after which blistering occurs. Intralesional immunotherapy with skin-test antigens (i.e., mumps, Candida, or Trichophyton antigens) may lead to the resolution both of the injected wart and other warts that were not injected. Contact immunotherapy using dinitrochlorobenzene, squaric acid dibutylester, and diphenylcyclopropenone may be applied to the skin to sensitize the patient and then to the lesion to induce an immune response. Intralesional bleomycin or laser therapy are also useful for recalcitrant warts. SOR C

Complementary and Alternative Therapy

• Although many complementary and alternative therapies are promoted for wart therapy, there is no significant data supporting their use in the treatment of plantar warts.

• Tools used for paring down warts, such as nail files and pumice stones, should not be used on normal skin or by other people.

Most plantar warts will spontaneously disappear without treatment. Treatment often hastens resolution of lesions.

• Regular follow-up to assess treatment efficacy, adverse reactions, and patient tolerance are recommended to minimize treatment dropouts.

• Because spontaneous regression occurs, observation of painless lesions without treatment is preferable.
• Therapy often takes weeks to months, so patience and perseverance are essential for successful therapy.

Patient Resources

• MayoClinic. Plantar Warts—http://www.mayoclinic.com/health/plantar-warts/DS00509.
• MedlinePlus. Warts—http://www.nlm.nih.gov/medlineplus/warts.html.
• Fort Drum Medical Activity. Patient Education Handouts: Warts and Plantar Warts—http://www.drum.amedd.army.mil/pt_info/handouts/warts_Plantar.pdf.

Provider Resources

• Bacelieri R, Johnson SM. Cutaneous warts: an evidence-based approach to therapy. Am Fam Physician. 2005;72(4):647-652—http://www.aafp.org/afp/20050815/647.html.
• Medscape. Nongenital Warts—http://emedicine.medscape.com/article/1133317.