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Chapter: Clinical Dermatology: Infections

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Viral infections: Viral warts

Most people will have a wart at some time in their lives. Their prevalence is highest in childhood, and they affect an estimated 4 –5% of schoolchildren in the UK.

Viral infections

The viral infections dealt with here are those that are commonly seen in dermatology clinics. A textbook of infectious diseases should be consulted for details of systemic viral infections, many of which, like measles and German measles, have their own specific rashes.

Viral warts

Most people will have a wart at some time in their lives. Their prevalence is highest in childhood, and they affect an estimated 4 –5% of schoolchildren in the UK.


Warts are caused by the human papilloma virus (HPV), which has still not been cultured in vitro

Nevertheless, more than 70 ‘types’ of the virus have been recognized by DNA sequencing; each has its own range of clin-ical manifestations. HPV-1, 2 and 4, for example, are found in common warts, whereas HPV-3 is found in plane warts, and HPV-6, 11, 16 and 18 are most common in genital warts. Infections occur when wart virus in skin scales comes into contact with breaches in the skin or mucous membranes.


Warts adopt a variety of patterns (Fig. 14.17), some of which are described below.

Common warts (Figs 14.18 and 14.19). The first signis a smooth skin-coloured papule, often more easily felt than seen. As the lesion enlarges, its irregular hyper-keratotic surface gives it the classic ‘warty’ appearance. Common warts usually occur on the hands but are also often on the face and genitals. They are more often multiple than single. Pain is rare.

Plantar warts. These have a rough surface, which pro-trudes only slightly from the skin and is surrounded by a horny collar (Fig. 14.20). On paring, the presence of bleeding capillary loops allows plantar warts to be distinguished from corns. Often multiple, plantar warts can be painful.

Mosaic warts (Fig. 14.21). These rough marginatedplaques are made up of many small tightly packed but discrete individual warts. They are most common on the soles but are also seen on palms and around fingernails. Usually they are not painful.

Plane warts (Fig. 14.22). These smooth flat-toppedpapules are most common on the face and brow, and on the backs of the hands. Usually skin-coloured or light brown, they become inflamed as a result of an immunological reaction, just before they resolve spontaneously. Lesions are multiple, painless and, like common warts, are sometimes arranged along a scratch line. 

Facial warts. These are most common in the beardarea of adult males and are spread by shaving. A digitate appearance is common. Lesions are often ugly but are painless.

Anogenital warts (condyloma acuminata) (Fig. 14.23).Papillomatous cauliflower-like lesions, with a moist macerated vascular surface, can appear anywhere in this area. They may coalesce to form huge lesions causing discomfort and irritation. The vaginal and anorectal mucosae may be affected. The presence of anogenital warts in children raises the spectre of sexual abuse, but is usually caused by autoinoculation from common warts elsewhere.


Warts resolve spontaneously in the healthy as the immune response overcomes the infection. This hap-pens within 6 months in some 30% of patients, and within 2 years in 65%. Such spontaneous resolution, sometimes heralded by a punctate blackening caused by capillary thrombosis (Fig. 14.24), leaves no trace. Mosaic warts are notoriously slow to resolve and often resist all treatments. Warts persist and spread in immunocompromised patients (e.g. those on immuno-suppressive therapy or with lymphoreticular disease).

Seventy per cent of renal allograft recipients will have warts 5 years after transplantation.


1 Some plantar warts are very painful.

2  Epidermodysplasia verruciformis is a rare inherited disorder in which there is a universal wart infection, usually with HPV of unusual types. An impairment of cell-mediated immunity  is commonly found and ensuing carcinomatous change frequently occurs. 3 Malignant change is otherwise rare, although infec-tions with HPV of certain genital strains predispose to cervical and penile carcinoma. HPV infections in immunocompromised patients (e.g. renal allograft recipients) have also been linked with skin cancer, especially on light-exposed areas.

Differential diagnosis

Most warts are easily recognized. The following must be ruled out.

   Molluscum contagiosum are smooth,dome-shaped and pearly, with central umbilication.

   Plantar corns are found on pressure areas; there isno capillary bleeding on paring. They have a central keratotic core and are painful.

   Granuloma annulare lesions  have a smoothsurface, as the lesions are dermal; and their outline is often annular.

Condyloma lata are seen in syphilis. They are rarebut should not be confused with condyloma acuminata (warts). The lesions are flatter, greyer and less well defined. If in doubt, look for other signs of secondary syphilis and carry out serological tests.

   Amelanotic melanomas and other epithelial malig-nancies can present as verrucose nodulesathose inpatients over the age of 40 years should be examined with special care. Mistakes have been made in the past.


Many warts give no trouble, need no treatment and will go away by themselves. Otherwise treatment will depend on the type of wart. In general terms, destruc-tion by cryotherapy is less likely to cause scars than excision or electrosurgery.

Palmoplantar warts

Home treatment is best, with one of the many wart paints now available. Most contain salicylic acid (12–20%). The success rate is good if the patient is prepared to persist with regular treatment. Paints should be applied once daily, after moistening the warts in hot water for at least 5 min. After drying, dead tissue and old paint are removed with an emery board or pumice stone. Enough paint to cover the surface of the wart, but not the surround-ing skin, is applied and allowed to dry. Warts on the plantar surface should be covered with plasters although this is not necessary elsewhere. Side-effects are rare if these instructions are followed. Wart paints should not be applied to facial or anogenital skin, or to patients with adjacent eczema.

If no progress is being made after the regular and correct use of a salicylic acid wart paint for 12 weeks, then a paint containing formaldehyde or glutaraldehyde is worth trying. A useful way of dealing with multiple small plantar warts is for the area to be soaked for 10 min each night in a 4% formalin solution, although a few patients become allergic to this.

Cryotherapy with liquid nitrogen (at –196°C) is more effective than the less cold, dry ice or dimethyl ether/propane techniques. However, it is painful. A cotton-tipped applicator dipped into liquid nitrogen is applied to the wart until a small frozen halo appears in the surrounding normal skin (Fig. 14.25). The human papilloma virus, and also other viruses such as HIV, can survive in stored liquid nitrogen and so, once used, a bud should not be dipped back into the flask. Treatment with a liquid nitrogen spray gun does not increases the clearance rate of plantar warts but not of hand warts. 

If further treatments are necessary, the optimal interval is 3 weeks. The cure rate is higher if plantar warts are pared before they are frozen, but this makes no difference to warts elsewhere. If there has been no improvement after four or five treatments there is little to be gained from further freezings.

A few minutes tuition from a dermatologist will help practitioners wishing to start cryotherapy. Blisters should not be provoked intentionally, but occur from time to time, and will not alarm patients who have been forewarned.

Anogenital warts

Women with anogenital warts, or who are the part-ners of men with anogenital warts, should have their cervical cytology checked regularly as the wart virus can cause cervical cancer.

The focus has shifted towards self-treatment using podophyllotoxin (0.5% solution or 0.15% cream) or imiquimod (5% cream). Both are irritants and should be used carefully according to the manufacturer’s instruc-tions. Imiquimod is an immune response modifier that induces keratinocytes to produce cytokines, leading to wart regression, and may help to build cell-mediated immunity for longlasting protection. It is applied as a thin layer three times weekly and washed off with a mild soap 6–10 h after application. Podophyllin paint (15%) is used much less often now. It should be applied carefully to the warts and allowed to dry before powdering with talcum. On the first occasion it should be washed off with soap and water after 2 h but, if there has been little discomfort, this can be increased stepwise to 6 h. Treatment is best carried out weekly by a doctor or nurse, but not by the pati-ent. Podophyllin must not be used in pregnancy. Cryotherapy, electrosurgery and laser treatment are all effective treatments in the clinic.

Facial common warts

These are best treated with electrocautery or a hyfrecator, but also surrender to careful cryotherapy. Scarring is an unwanted complication. Shaving, if essential, should be with a brushless foam and a dis-posable razor.

Plane warts

On the face these are best left untreated and the patient or parent can be reasonably assured that spontaneous resolution will occur. When treatment is demanded, the use of a wart paint or imiquimod cream is reason-able. Gentle cryotherapy of just a few warts may help to induce immunity.

Solitary, stubborn or painful warts

These can be removed under local anaesthetic with a curette, although cure is not assured with this or any other method, and a scar often follows. Surgical excision is never justifiable (Fig. 14.26). Bleomycin can also be injected into such warts with success but this treatment should only be undertaken by a specialist.


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