Diagnosis: Common Warts

Common warts (verrucae vulgaris) are caused by the human papillomavirus (HPV). Hand warts are most commonly caused by HPV-2 and foot warts are most commonly caused by HPV-1, although other HPV types can also cause warts in these locations. Warts occur in up to 10% of children and young adults in the United States. Most warts develop in patients 12-16 years of age; the peak incidence is at age 13 in females and age 14.5 years in males.1

Although some warts can disappear spontaneously,1-3 treatment is often needed because failure to shrink warts facilitates further spread. The size and distribution of warts typically continue to increase with time. Moreover, the longer a wart is present, the more treatment-resistant it becomes. It should be noted that most skin infected with HPV does not clinically manifest a wart but is still infective. The reason for this dichotomy is unclear.

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Warts can be painful, depending on their location (e.g., soles of the feet and near the nails), and they can be socially unacceptable when located on areas open to view (e.g., hands and face).3 Moreover, treatment can result in unsightly scarring.3

No single medical therapy or destructive modality achieves complete remission in every patient.1 All therapies must be directed toward increasing local inflammation because a prime reason for the body’s inability to clear warts is that they engender their own immunologic invisibility, preventing the immune system from driving them into quiescence.

Destructive modalities include cryotherapy, electrodesiccation, carbon dioxide laser, pulsed dye laser, photodynamic therapy, or surgical removal. The most commonly used destructive modality is cryotherapy. Studies have shown that a 10-second application of cryotherapy with two freeze/thaw cycles is more effective than shorter applications for plantar warts but not for palmar warts4 and that the percentage cure is related to the number of treatments independent of the time interval between them.5 I find a cryospray gun to be more effective than a cotton-wool bud for the application of liquid nitrogen.

Topical therapies can be patient-applied (5-fluorouracil, salicylic acid, retinoids, and imiquimod) or clinician-applied (podophyllin, squaric acid, cantharidin, formaldehyde [formalin], and glutaral [glutaraldehyde]). Salicylic acid is a useful treatment for warts. OTC preparations are <17% salicylic acid, whereas physician-prescribed preparations can contain as much as 70% salicylic acid. According to a Cochrane review, salicylic acid is safe and effective and no clear evidence exists to prove that other therapies are superior.6 I think imiquimod can be effective if it is applied daily under occlusion to the eroded bases of warts that have been turned first into bullae following liquid nitrogen-induced tissue damage and burst, with thin pink skin at their bases.

Children younger than 12 do not tolerate the pain of cryotherapy very well. Therefore, salicylic acid-podophyllin-cantharidin combinations can be helpful for treating warts (81% effectiveness in one study7) in young patients.8 

Additional therapies include intralesional injection of interferons, immunotherapy (Candida antigen), and bleomycin. Intralesional immunotherapy9 with Candida skin antigen consists of a 0.1-cc injection of antigen into the largest wart, followed several weeks later by injection of 0.1 cc into each of two to three warts. I have had occasional success with the 30 patients in whom I have used it. Oral isotretinoin and oral cimetidine (at a dose of 20 mg/kg/day) have been reported effective, although I have not found them so. Duct tape is not an effective treatment for warts. Some claim (my experience to the contrary) that positive suggestion, treatment simulations, and hypnosis are effective for warts and that these should be tried in children, as these approaches are noninvasive. 

Potential side effects to wart treatment include pain and hemorrhagic bullae following cryosurgery. Bleomycin sulfate (1 mg/mL sterile saline solution) injected into warts is effective but is best not used in children because its side effects include pain during and after treatment, pigment changes, Raynaud phenomenon, necrotic eschar, scarring, and nail damage.