Warts are small, skin-coloured cutaneous lesions that affect the epidermis of the skin, caused by HPV infection. Over 100 types of HPV have been identified, and the site and type of the lesion depends on the type of HPV involved. Mucous membranes and the anogenital region can be affected.
HPV warts are benign, but are sometimes associated with cervical, anal, genital and oropharyngeal carcinomas. Estimates suggest a prevalence of 4-5 per cent in children and adolescents, and 3 per cent in adults. They are uncommon in babies.
Infection may be by direct skin contact or fomites left on surfaces such as towels and floors. Wetting or roughening of the skin increases the risk of infection. Atopic eczema and immunosuppression are also known risk factors.
Warts can usually be diagnosed on examination. But there are a number of other conditions that may need to be considered, including solar keratosis and squamous cell carcinoma (see box below, left).
Plantar or periungual warts can be painful, but most other types are not. There are four main types. Common warts are roughened papules, presenting singly or in groups, commonly seen on the hands, elbows and knees although they can occur anywhere.
Plane warts, also called flat warts, occur singly or in groups of up to 100. They are much more common in children than adults, and occur on the hands, face or legs. They may be flesh-coloured or pigmented.
Plantar warts (verrucas) occur on the sole of the foot, heel or toes. They are rough, keratotic, sharply-defined lesions. On paring them down, black dots representing thrombosed capillaries can be seen. They often occur individually but may coalesce (mosaic warts).
Filiform warts are finger-like warts most commonly seen as clusters occurring on the face.
Around two thirds of warts resolve spontaneously within two years, and patients may be happy with a 'wait and see' approach.
Spread can be limited by keeping the wart covered with a waterproof dressing when swimming and in changing rooms, not sharing towels, shoes or socks, keeping the feet dry and changing socks daily.
Treatment options in primary care include salicylic acid and cryotherapy.
Salicylic acid treatment is available OTC. Two thirds of lesions treated with salicylic acid resolve within 12 weeks. Strength varies from 11 per cent, which is suitable for all sites except the face, to 50 per cent, which is suitable only for the feet.
Occlusive dressings for plantar warts may improve effectiveness. The wart should be softened by soaking it in warm water and any previous preparation should be removed prior to application.
The area should be debrided of hard skin twice a week using a disposable nail file, or more frequently if soreness does not develop. Salicylic acid should be avoided in patients with diabetes and any patient with peripheral vascular disease.
Treatment using duct tape is worth trying in those patients who do not want more aggressive therapy. Duct tape causes local irritation, which stimulates the patient's immune system to destroy the wart. The tape is applied for six days, then removed and the wart soaked in water. It should then be gently debrided and left uncovered overnight. The treatment may take up to two months to work.
Cryotherapy is as effective as salicylic acid but may be more convenient for multiple small warts. Many GPs run clinics using liquid nitrogen. It can be applied as a spray or using a cotton bud. The latter may be more suitable for children and for treating lesions near eyes.
The liquid is applied until a 'halo' develops around the lesion. Application is then continued for a further 5-30 seconds. Scrupulous precautions must be taken to prevent cross-infection. Limited evidence suggests two freeze-thaw cycles are more effective than one, but increase the risk of pain and blistering. A three-week interval between treatments is commonly used.
Reasons to refer to secondary care include persistence of warts, presence of peripheral vascular disorders or immunosuppressive conditions.
Carbon dioxide or pulsed dye laser treatment may also be used in secondary care. This is suitable for periungual or subungual warts. Photodynamic therapy can also be used. It depends on abnormal cells taking up a chemical that destroys the cells when activated by light.
Anti-mitotic treatments including podophyllin or podophyllotoxin are useful for anogenital warts but less effective on ordinary skin where the stratum corneum is thickened. Topical or oral retinoids can reduce the bulk of a wart, but there are limited data supporting their benefits in clearing warts.
Immunomodulators including topical sensitisers such as dinitrochlorobenzene and imiquod are useful in immunosuppressed patients. Intralesional interferon is mainly used for genital warts.
Virucidal treatments such as formaldehyde do not affect the circulation and are useful for patients with diabetes or peripheral vascular disease.
Dr Knott is a GP in Enfield, London
Conditions to be excluded in diagnosing warts:
- Molluscum contagiosum
- Pigmented naevus (mole)
- Seborrhoeic keratosis
- Fibroepithelial polyp (skin tag)
- Solar keratosis (actinic keratosis)
- Squamous cell carcinoma
- Lichen planus
- Corns and calluses
- Verrucous squamous cell carcinoma
- Warts are common benign lesions caused by HPV.
- They can occasionally be associated with carcinomas.
- Two thirds will resolve spontaneously within two years.
- Most warts can be treated in primary care.
- Referral is appropriate for patients with persistent warts, conditions affecting the peripheral circulation, and where there is diagnostic difficulty.
- PRODIGY guidance: Warts (including verrucas), 2006. www.cks.library.nhs.uk/warts_including_verrucas
- Gibbs S, Harvey I. Topical treatments for cutaneous warts. Cochrane Database Syst Rev. 2001, Issue 2 CD001781.