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Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1996. Updated by Dr Jannet Gomez, Postgraduate student in Clinical Dermatology, Queen Mary University London, UK, December 2016.
A viral wart is a very common growth of the skin caused by infection with human papillomavirus (HPV). A wart is also called a verruca, and warty lesions may be described as verrucous.
Warts are particularly common in:
Warts are due to infection by the human papillomavirus (HPV), a DNA virus. More than 100 HPV subtypes are known, giving rise to a variety of presentations. Infection occurs in the superficial layers of the epidermis, causing proliferation of the keratinocytes (skin cells) and hyperkeratosis — the wart. The most common subtypes of HPV are types 2, 3, 4, 27, 29, and 57.
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.
Cutaneous viral warts have a hard, keratinous surface. A tiny black dot may be observed in the middle of each scaly spot, due to an intracorneal haemorrhage.
Common warts present as papules with a rough, papillomatous and hyperkeratotic surface ranging in size from 1 mm to larger than 1 cm. They 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, and clusters of less painful mosaic warts. Plantar epidermoid cysts are associated with warts. Persistent plantar warts may rarely be complicated by the development of verrucous carcinoma.
Plane warts have a flat surface. The most common sites are the face, hands and shins. They are often numerous. They may be inoculated by shaving or scratching so that they appear in a linear distribution (pseudo-Koebner response). Plane warts are mostly caused by HPV types 3 and 10.
Filiform warts are on a long stalk like a thread. They commonly appear on the face. They are also described as digitate (like a finger).
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.
Tests are rarely needed to diagnose viral warts, as they are so common and have a characteristic appearance.
Many people don't bother to treat viral warts because treatment can be more uncomfortable than warts —they are hardly ever a serious problem. Warts that are very small and not troublesome can be left alone, and in some cases, they will regress on its own.
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 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.
The paint is 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.
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 repeated at one to two–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. Read and follow the instructions carefully.
Combining immunotherapy with cryotherapy reduces the number of cryotherapy sessions.
Electrosurgery (curettage and cautery) is used for large and resistant 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 recurrent, resistant or extensive warts include:
HPV vaccines are available to prevent anogenital warts. Anecdotally, these have been reported to result in the clearance of non-genital warts in some people without definite evidence that the vaccine is the cause of remission. In New Zealand, 12-year-old girls and boys are vaccinated against nine strains of HPV.
No treatment is universally effective at eradicating viral warts. In children, even without treatment, 50% of warts disappear within six months, and 90% are gone in 2 years. They are more persistent in adults, but they clear up eventually. They are likely to recur in patients that are immune suppressed, for example, organ transplant recipients. Recurrence is more frequent in tobacco smokers.
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