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Introduction

Plantar warts can be a frustrating problem for both patients and doctors alike. Although they are usually benign and resolve on their own, the stigma of having a wart often leads a patient to seek medical attention. Other times, the location of the wart may cause so much pain that a patient has few other options than to schedule an appointment with their podiatrist. Either way, having the wart checked out by a medical professional is always a good idea-it may not be a wart after all. Unfortunately, warts can be difficult to eradicate and often return months or years later. Although warts have this tendency to recur, many effective treatment options and preventative measures exist to cure your current warts and help prevent future warts from appearing.

What are Warts?

Warts are a common viral infection caused by the Human Papilloma Virus (HPV). HPV has over 75 known subtypes-three of which have been implicated as causative agents in the "plantar wart" (medical term: verruca plantaris). Plantar warts are named for the location they are found, the bottom (plantar surface) of the foot. HPV has an incubation period ranging from 4 weeks to 20 months [1]. It thrives in warm, moist environments and is spread through direct contact of the skin with a contaminated surface. The virus enters the skin through small, often invisible breaks or cracks on the skin surface. Walking barefoot in a public shower is the most commonly cited example, but HPV can be contracted almost anywhere [2]. Some lucky individuals are immune to HPV infection, while less fortunate others are plagued with recurrences of the same infection.

Warts affect about 7% of Americans each year [3]. Although warts can occur at any age, HPV has a strong predilection for teenagers. Excess moisture from sweat can macerate (soften) the skin making it easier for the virus to penetrate and settle. Thus, having sweaty feet, often linked to the increased activity of adolescence, contributes to the problem. Furthermore, adolescents are frequently exposed to public locker rooms and showers at schools and camps-ideal sites to contract HPV.

Appearance and Diagnosis

Clinically, warts are classified according to their location and appearance on the skin. Warts can appear anywhere on the body; only those appearing on the bottom of the foot are referred to as plantar warts. Warts are usually painful when they are on a weight-bearing surface or at a place of increased irritation.

Plantar warts are endophitic in nature, meaning they grow into and not out of the skin. Moreover, being on a weight-bearing surface (i.e., the ball of the foot, bottom of the toes, and/or heel), plantar warts are constantly pushed deeper into the skin just by standing. Likened to icebergs, only a small portion of a wart can be seen above the skin surface; it is impossible to know how deep it goes simply by looking at it. This makes treatment very difficult, as the wart may be deeper than the selected treatment can penetrate.

Warts can appear as small, raised flesh-colored lesions with a cauliflower shaped head, or as flat, callused islands or patches. Plantar warts typically appear as the latter. They may appear alone or in clusters known as "mosaic" warts. Left untreated, a single wart can grow to more than an inch in circumference. Plantar warts can look and feel very similar to simple callus formation (a protective mechanism of the body); thus distinguishing between the two can be quite difficult.

Careful clinical examination can reveal several features that differentiate a wart from a callus. First, warts tend to be more painful when squeezed from side-to-side, whereas a callus will hurt more on direct pressure. Second, the trained eye of your doctor may appreciate a discontinuation of the skin lines indicative of a wart; calluses will often have skin lines (like fingerprints) intact. Last, warts have a very superficial blood supply comprised of tiny capillary networks. These capillaries may appear as minute black specs under bright light, but are best visualized when the doctor trims away (often without pain) the dead skin. Because the blood supply is very superficial, warts will bleed in a pinpoint fashion. Calluses do not have their own blood supply and therefore do not bleed as frequently. It should be noted that the pinpoint bleeding associated with a wart might also appear with mere scratching of the lesion. Since the virus is contained in the blood, scratching to the point of bleeding could transfer the virus to another location (like your scratching finger).

In some instances a doctor may want to biopsy a lesion in order to ensure a diagnosis. In rare instances warts can transform into cancerous lesions, especially in individuals with compromised immune systems. It is always a good idea to have any suspicious or long-standing lesions examined by your physician.

Treatment Options

There are many factors considered in choosing an appropriate treatment for verrucae. Determining the best way to treat them usually depends upon such factors as size, number, and location, as well as pain, immunologic status and previous treatments. Studies have shown that approximately 65% of all warts in healthy individuals resolve spontaneously (without treatment) within two years [4, 5]. For this reason some doctors and patients elect to leave asymptomatic warts alone.

The decision to treat a wart, rather than waiting for it to disappear on its own, is often a smart one. Treatment serves three main goals: decrease symptomatology, decrease duration, and decrease further transmission. Doctors have a plethora of treatment choices at their disposal and will work with you to select the most appropriate, and hopefully effective, therapy.

Topical medications such as salicylic acid, 5-flourouracil, and cryogens (freezing agents), generally function to stimulate the patient's immune system by triggering a response at the wart site, and ideally clearing the virus from the skin cells. Some of these topical options (commonly salicylic acid) are available over-the-counter at your local pharmacy. Care should be taken in using these products, since the medication will work on whatever skin it comes in contact with, including healthy skin. For this reason, it is recommended that diabetics and other individuals with decreased sensation not use these products without medical supervision. Topical medications have proven to be anywhere from 45 to 86% effective depending upon the number and location of lesions [6, 7]. Many doctors will use a combination therapy-first freezing the wart with liquid nitrogen or other cryogen, and then applying salicylic acid to the lesion. Patients can then continue to apply the acid as directed between visits.

When topical treatments fail, more aggressive surgical procedures are considered. These procedures, performed under local anesthesia, include sharp excision (cutting off the lesion), hyfercation (burning off the lesion), and laser destruction (zapping off the lesion). These procedures are generally painless (since the affected area is numbed beforehand) and may not limit activity afterward. It should be noted that removing the wart with these more aggressive therapies still cannot guarantee its permanent eradication. Often times the virus will retreat and/or lie dormant in the skin cells surrounding the original lesion, only to return at a later time.

Latest Treatment

Within recent years, research on the orally taken drug cimetidine (more commonly known as Tagamet-a medication for stomach ulcers) has shown some promise in the treatment of warts. Cimetidine is an H2 receptor blocker used primarily to decrease histamine stimulation of gastric acid secretion in the gut-this is far from foot indeed. So why does it work on warts? Cimetidine also inhibits the H2 receptors found on specific cells thought to be a factor in limiting the immune response that would destroy the virus [8, 9, 10]. The function of these cells, known as suppressor T cells, is prevented by cimetidine thereby allowing the body to rid itself of the virus.

Studies have indicated that cimetidine works best in patients under the age of 17-showing a complete resolution of the lesions in 80% of patients after two to four months of therapy [10]. The success rate among patients over the age of 17 is considerably less at about 30%. The dosage of cimetidine required for the treatment of plantar warts is different than its over-the-counter counterpart Tagamet, and is often specifically calculated by your physician based on patient age and body weight. As with most other oral medications, cimetidine has some side effects and drug interactions that your doctor will discuss before writing a prescription. Some common side effects include headache, diarrhea, dizziness, and nausea. Your doctor can help you determine if cimetidine may work for you.

Prevention

The most effective treatment for warts is avoiding them. The American Podiatric Medical Association [11] provides the following tips for prevention:

• Avoid walking barefoot (including public locker rooms, showers, and restrooms).
• Clean your feet daily and dry them thoroughly after washing.
• Change your shoes regularly and your socks daily.
• Avoid direct contact with warts (whether they be on yourself or others).
• Inspect your skin-have new lesions or changes in your skin examined by a medical professional.
• If you have children, check their feet periodically.

Conclusion

If you think that you have developed a wart, do not despair. It is not an indicator of overall cleanliness and it does not relate to kissing frogs. Plantar warts are among the most common foot problems that podiatrists see. If your doctor determines that you indeed have a wart, he or she has an entire arsenal of effective treatment options from which to choose. If your wart seems to take a long time to resolve, don't get discouraged. Most warts eventually resolve without treatment, and in children, the lesions often times don't carry over into adulthood. A simple visit to your neighborhood podiatrist can answer any questions you have and get you on a quicker road to recovery. Until then, keep your feet dry and wear flip-flops in your local public shower.

References

1. Androphy EJ: Human papillomavirus: Current concepts. Arch Dermatol, 125(5): 683-685, 1989.
2. Johnson LW: Communal showers and the risk of plantar warts. J Fam Pract, 40(2): 136-8, 1995.
3. Robbins JE: Primary Podiatric Medical Book. WB Saunders, Philadelphia, p.302, 1994.
4. Benten C: The management of viral warts. The Practitioner, 232: 933-938, 1988.
5. Ricketti JC, Niedbala RS: Histofreezer: A study of a new method of cryosurgical treatment of verrucae plantaris. The Lower Extremity, 2(3): 167-171, 1995.
6. Bart BJ et al: Salicylic acid in karaya gum patch as a treatment for verruca vulgaris. J Am Acad Dermatol, 20(1): 74-76, 1989.
7. Bunney MH et al: The treatment of resistant warts with intralesional bleomycin: Controlled clinical trial. Br J Dermatol, 111(2): 197-207, 1984.
8. Melvin D, Barnes CL: Cimetidine for the treatment of Viral Warts. US Pharmacist: H22-24, June 1995.
9. Kumar A: Cimetidine: an immunomodulator. DICP, 24(3): 289-295, 1990.
10. Orlow SJ, Paller A: Cimetidine therapy for multiple viral warts in children. J Am Acad Dermatol, 28(5 Pt 1): 794-796, 1993.
11. American Podiatric Medical Association. APMA.org, 2000.

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