Plantar wart

Classification and external resources
A plantar wart. Striae (fingerprints) go around the lesion.
ICD-10	B07
ICD-9	078.12

A plantar wart, verruca or myrmecia (formally, a verruca plantaris^[1]:405) is a wart caused by the human papillomavirus (HPV) occurring on the sole (Latin planta) or toes of the foot. (HPV infections in other locations are not plantar; see human papillomavirus.) Plantar warts are usually self-limiting, but treatment is generally recommended to lessen symptoms (which may include pain), decrease duration, and reduce transmission.^[2]
Infection occurs in an estimated 7–10% of the US population. In a 1949 survey of 3,906 mainland Chinese and 1,222 Indians who had never worn shoes, plantar warts were reported in 0.29% of subjects. ^[3] While lower than rates in the US, this alone does not establish a causal relationship between shoe usage and incidence rate of plantar warts; genetics plays an important role in determining susceptibility. Common warts appear approximately twice as frequently,^[4]

Contents

Cause

Mosaic warts cluster

Young plantar warts

Plantar warts are benign epithelial tumors generally caused by infection by human papilloma virus types 1, 2, 4, 60, or 63,^[5] but have also been caused by types 57,^[6] 65,^[7] 66,^[8] and 156.^[9] These types are classified as clinical (visible symptoms). The virus attacks compromised skin through direct contact, entering through possibly tiny cuts and abrasions in the stratum corneum (outermost layer of skin). After infection, warts may not become visible for several weeks or months. Because of pressure on the sole of the foot or finger, the wart is pushed inward and a layer of hard skin may form over the wart. A plantar wart can be painful if left untreated.^[2][10]
Warts may spread through autoinoculation, by infecting nearby skin or by infected walking surfaces. They may fuse or develop into clusters called mosaic warts.^[5]

Diagnosis

A plantar wart is a small lesion that appears on the sole of the foot and typically resembles a cauliflower, with tiny black petechiae (tiny hemorrhages under the skin) in the center. Pinpoint bleeding may occur when these are scratched, and they may be painful when standing or walking.
Plantar warts are often similar to calluses or corns, but can be differentiated by close observation of skin striations. Feet are covered in skin striae, which are akin to fingerprints on the feet. Skin striae go around plantar warts; if the lesion is not a plantar wart, the striations continue across the top layer of the skin. Plantar warts tend to be painful on application of pressure from either side of the lesion rather than direct pressure, unlike calluses (which tend to be painful on direct pressure instead).

Prevention

HPV is spread by direct and indirect contact from an infected host. Avoiding direct contact with infected surfaces such as communal changing rooms and shower floors and benches, avoiding sharing of shoes and socks and avoiding contact with warts on other parts of the body and on the bodies of others may help reduce the spread of infection. Infection is less common among adults than children.^[10]
As all warts are contagious, precautions should be taken to avoid spreading them. The British National Health Service recommends that children with warts:

• cover them with an adhesive bandage while swimming
• wear flip-flops when using communal showers
• should not share towels.^[11]

Plantar warts are not prevented by inoculation with currently available HPV vaccines, because the warts are caused by different strains of the human papillomavirus. Gardasil protects against strains 6, 11, 16, and 18; and Cervarix protects against 16 and 18; whereas plantar warts are caused by strains 1, 2, 4, and 63.

Treatment

Conventional treatments that have been found to be effective^[12] include:

First-line therapy	Over the counter salicylic acid
Second-line therapy	Cryosurgery, intralesional immunotherapy, or pulsed dye laser therapy
Third-line therapy	Bleomycin, surgical excision

Medications

Salicylic acid—The treatment of warts by keratolysis involves the peeling away of dead surface skin cells with Keratolytic chemicals such as salicylic acid or trichloroacetic acid. These are available in over-the-counter products or, in higher concentrations, may need to be prescribed by a physician. A 12 week daily treatment with salicylic acid has been shown to lead to a complete clearance of warts in 10–15% of the cases.^[13]
Cantharadin (blister beetle extract) applied to a wart by a doctor causes a blister after 4–6 hours. One formulation is known as Cantharone (0.7% Cantharidin); a more powerful one is Cantharone PLUS which contains the same active ingredient as Cantharone, but it also contains Podophyllin (5%) and Salicylic Acid (30%).
Immunotherapy—Intralesional injection of antigens (mumps, candida or trichophytin antigens USP) is a new wart treatment which may trigger a host immune response to the wart virus, resulting in wart resolution. It is now recommended as a second-line therapy.^[14]

Surgery

A ~7mm plantar wart surgically removed from patient's footsole after other treatments failed

Liquid nitrogen—This, and similar cryosurgery methods, is a common surgical treatment which act by freezing the internal cell structure of the warts, destroying the live tissue. Up to three sessions may be required.
Electrodesiccation and surgical excision may produce scarring.
Laser surgery—This is generally a last resort treatment, as it is expensive and painful, but may be necessary for large, hard-to-cure warts.^[15]
Cauterization—This may be effective as a prolonged treatment. As a short-term treatment, cauterization of the base with anaesthetic can be effective, but this method risks scars or keloids. Subsequent surgical removal is unnecessary, and risks keloids and recurrence in the operative scar.^[16]

Relative effectiveness

A 2006 review of the effects of different local treatments for cutaneous, non-genital warts in healthy people concluded: ^[17]

• there is a lack of evidence (many trials were excluded because of poor methodology and reporting).
• the average cure rate using a placebo was 27% after an average period of 15 weeks.
• the best treatments are those containing salicylic acid. They are clearly better than placebo.
• there is little clinical trial data for the absolute efficacy of cryotherapy
• two trials comparing salicylic acid and cryotherapy showed no significant difference in efficacy.