What are viral warts?
Warts are very common non-cancerous growths of the skin caused by infection with human papillomavirus (HPV). More than 100 HPV subtypes are known, giving rise to a variety of presentations.
A viral wart on the sole of the foot is also called a verruca, and warty lesions are often described as verrucous.
Who gets viral warts?
Warts are particularly common in school-aged children, but they may arise at any age. They are more persistent and numerous in people that are immune suppressed with medications such as azathioprine or ciclosporin, or with human immunodeficiency virus (HIV) infection. In these patients, the warts almost never disappear despite treatment.
What causes viral warts?
HPV is spread by direct skin-to-skin contact or autoinoculation. This means if a wart is scratched or picked, the viral particles may be spread to another area of skin. The incubation period can be as long as twelve months.
What are the clinical features of viral warts?
Warts have a hard surface. A tiny black dot may be observed in the middle of each scaly spot, due to a thrombosed capillary blood vessel.
Common warts arise most often on the backs of fingers or toes, around the nails—where they can distort nail growth—and on the knees. Sometimes they resemble a cauliflower; these are known as butcher’s warts.
Plantar warts (verrucas) include tender inwardly growing and painful ‘myrmecia’ on the sole of the foot, and clusters of less painful mosaic warts.
Plane warts have a flat surface. They are often numerous and may be inoculated by shaving or scratching, so that they appear in a line.
Filiform warts are on a long stalk like a thread. They commonly appear on the face.
Complications of viral warts
Viral warts are very widespread in people with the rare inherited disorder epidermodysplasia verruciformis.
Malignant change is rare in common warts, and causes verrucous carcinoma.
Oncogenic strains of HPV, the cause of some anogenital warts and warts arising in the oropharynx, are responsible for intraepithelial and invasive neoplastic lesions including cervical, anal, penile and vulval cancer.
How are viral warts diagnosed?
Tests are rarely needed to diagnosis viral warts, as they are so common and have a characteristic appearance. Dermatoscopic examination is sometimes helpful to distinguish viral warts from other verrucous lesions such as seborrhoeic keratosis and skin cancer.
What is the treatment for viral warts?
Many people don't bother to treat viral warts because treatment can be more uncomfortable and troublesome than the warts—they are hardly ever a serious problem. However, warts may be painful, and they often look ugly so cause embarrassment.
To get rid of them, we have to stimulate the body's own immune system to attack the wart virus. Persistence with the treatment and patience is essential!
Topical treatment includes wart paints containing salicylic acid or similar compounds, which work by removing the dead surface skin cells. Podophyllin is a cytotoxic agent used in some products, and must not be used in pregnancy or in women considering pregnancy.
The paint is normally applied once daily. Treatment with wart paint usually makes the wart smaller and less uncomfortable; 70% of warts resolve within twelve weeks of daily applications.
- Soften the wart by soaking in a bath or bowl of hot soapy water.
- Rub the wart surface with a piece of pumice stone or emery board.
- Apply wart paint or gel accurately, allowing it to dry.
- Covered with plaster or duct tape.
If the wart paint makes the skin sore, stop treatment until the discomfort has settled, then recommence as above. Take care to keep the chemical off normal skin.
Cryotherapy is normally repeated at one to three week intervals. It is uncomfortable and may result in blistering for several day or weeks. Success is in the order of 70% after 3-4 months of regular freezing.
A hard freeze using liquid nitrogen might cause a permanent white mark or scar. It can also cause temporary numbness.
An aerosol spray with a mixture of dimethyl ether and propane (DMEP) can be purchased over the counter to freeze common and plantar warts. It is important to read and follow the instructions carefully.
Electrosurgery (curettage and cautery) is used for large warts. Under local anaesthetic, the growth is pared away and the base burned. The wound heals in two weeks or longer; even then 20% of warts can be expected to recur within a few months. This treatment leaves a permanent scar.
Other experimental treatments for warts include:
- Topical retinoids, such as tretinoin cream or adapalene gel
- Fluorouracil cream
- Bleomycin injections
- Photodynamic treatment
- Laser vaporisation
- Pulse dye laser destruction of feeding blood vessels
- The immune modulator imiquimod cream
- Immune stimulation using diphencyprone or squaric acid
- Oral retinoids
How can viral warts be prevented?
HPV vaccines are available to prevent anogenital warts. Anecdotally, these have been reported to result in clearance of non-genital warts in some people. New vaccines are under development that may reduce the risk of other types of HPV.
What is the outlook for viral warts?
No treatment is universally effective at eradicating viral warts. In children, even without treatment, 50% of warts disappear within 6 months, and 90% are gone in 2 years. They are more persistent in adults but they clear up eventually.