It is well known that warts are harmless and self-limiting and that the best treatment is to leave them alone if possible. But patients do not always see it like that.
A common problem is the child with prominent facial warts being teased relentlessly at school with the parents asking the doctor to do something to end this situation.
Many patients do not want to wait for the natural resolution of their warts.
As doctors we might therefore be expected to have some idea of how to deal with this common problem in a sensible way and have some sort of grasp on the effectiveness of different treatments.
Amazingly, this seems not to be the case, although a systematic review of the evidence might help us to get close to being able to do so.
Reviewing the data
Unlike a traditional review, where the author looks at a few research papers and trials and makes some personal, subjective and, possibly rather anecdotal, overarching comments, a systematic review involves looking at all the least-biased trial evidence in a thorough and organised way and trying to make some objective sense of it all.
This is what the Cochrane Skin Group attempted to do recently.
The questions that clinicians are particularly keen to have answered include: are salicylic acid (SA) paints at all effective? How often does cryotherapy really cure patients of their warts? Which of these two treatments is better at getting rid of warts? Are there any other treatments that work without being too dangerous or expensive?
The results of the review were a little surprising.
Most randomised trials of wart treatments are not done very well. Of 52 trials reviewed, 39 were of low quality, 10 of intermediate quality and only three of high quality.
Placebo treatments work well. On average, there was a cure rate of about 30 per cent of patients after about 10 weeks. SA was shown to be effective in 75 per cent of patients compared with 48 per cent with placebo.
Cryotherapy does not seem to be any more effective than much simpler, safer treatments - 62 per cent of patients were cured with SA compared with 65 per cent with cryotherapy.
Also, 71 per cent were cured with duct tape compared with 46 per cent with cryotherapy
Evidence for the absolute effectiveness of cryotherapy is lacking: 35 per cent of patients cured with cryotherapy compared with 34 per cent with placebo cream or no treatment.
However, the quality of the research is generally not of a high quality and overall conclusions are therefore made with some caution.
One of the best-conducted studies - in terms of methodology and reporting - on the use of placebo was carried out in primary care by GPs from Belfast.
Their study looked at the effect of monochloracetic acid crystals and 60% SA against placebo in 57 patients.
After six weeks, 19 patients in the treatment group were cured, compared to five in the placebo group; those treated had detectable secondary immune response.
Another interesting recurring theme is the high rate of cure with placebo treatments. This lends considerable weight to the argument for not treating warts at all, although it must be remembered that a placebo treatment is not the same thing as not giving any treatment.
Evidence for the efficacy of topical treatments containing SA is good and these treatments do appear to have a genuine therapeutic effect.
We can say that warts are more likely to disappear if they are regularly painted with SA, rather than with placebo, which is not ineffective.
Most of the trials used SA daily for two to three months. Therefore it seems sensible to advise patients to carry on for at least three months and preferably even longer.
SA preparations are not licensed for use in patients with diabetes or facial warts, although this is arguably an over-cautious view.
Freezing warts is usually performed in primary care and dermatology clinics.
But, again rather surprisingly, this old favourite did not fare well in a stringent review of the data. There is virtually no trial evidence for its absolute efficacy compared with placebo or no treatment.
Evidence (from two small trials of poor quality) suggests that it is no better than placebo.
Much greater weight should be attached to data from three trials that show cryotherapy to be as effective as simpler safer treatments.
Two trials comparing cryotherapy with SA showed them to be essentially equivalent in efficacy. The third, more recently published trial compared the treatment of occlusion with duct tape applied for a week at a time to the warts, with traditional cryotherapy given every two to three weeks for a maximum of six times.
The trial was properly randomised and blinded, but was rather small and had slightly non-ideal follow up arrangements. The cure rate using the less favourable intention-to-treat analysis was 71 per cent (22 out of 30 patients) for duct tape and only 46 per cent for cryotherapy.
The authors concluded that duct tape was superior to cryotherapy, but the small numbers and wide confidence interval in this trial make this a rather extravagant claim.
What this trial does show however is that it seems most unlikely that cryotherapy could be superior to duct tape.
Evidence-based medicine is, of course, only as good as the evidence that it utilises and the findings are tempered by a dearth of good-quality research.
Nonetheless it would seem rather difficult, in the light of the trials mentioned above even with their methodological shortcomings, to defend an important place for cryotherapy in managing common warts.
Other trials of more obscure, hazardous and expensive treatments for warts were found during a data search.
These include intralesional bleomycin, 5-fluorouracil, photodynamic therapy, interferons, the pulsed dye laser and dinitrochlorobenzene (DNCB).
Most of these trials are of low quality and some were contradictory in their findings, particularly those of bleomycin.
Except for DNCB, none of these treatments appear to have any advantage over simpler approaches like SA.
- Dr Gibbs is consultant dermatologist, Ipswich Hospital NHS Trust and a member of the Cochrane Skin Group
- If you have a special interest in dermatology, you can register for free copies of MIMS Dermatology at www.hayreg.co.uk/specials
STEP-BY-STEP APPROACH TO TREATING WARTS
- Leave well alone and await spontaneous resolution.
- Warts can be filed down weekly to keep them out of the way on the hands and reduce pain on the soles.
- Use SA paint or duct tape occlusion for at least three months.
- Possibly try cryotherapy, although there is no convincing trial evidence that it is any better than above suggestions.
- Either give up and keep patients comfortable (as the first point above) or, possibly consider referral for alternative treatments such as DNCB if available.
- More randomised trials of higher quality are needed.
- Gibbs S, Harvey I, Sterling J, Stark R. Local treatments for cutaneous warts: systematic review. BMJ 2002; 325: 461-4.
- Gibbs S, Harvey I, Sterling J, Stark R. Local treatments for cutaneous warts (Cochrane Review). In: The Cochrane Library, Issue 3, 2003. Oxford: Update Software.
- Steele K, Shirodaria P, O'Hare M, Merrett J D, Irwin W G, Simpson DI et al. Monochloroacetic acid and 60% salicylic acid as a treatment for simple plantar warts: effectiveness and mode of action. Br J Derm 1988; 118: 537-43.
- Gibson J R, Harvey S G, Barth J, Darley C R, Reshad H, Burke C A. A comparison of acyclovir cream versus placebo cream versus liquid nitrogen in the treatment of viral plantar warts. Dermatologica 1984;168:178-81.
- Wilson P. Immunotherapy v cryotherapy for hand warts; a controlled trial (abstract). Scottish Med J 1983; 28: 191.
- Bunney M H, Nolan M W, Williams D A. An assessment of methods of treating viral warts by comparative treatment trials based on a standard design. Br J Derm 1976; 94: 667-798.
- Steele K, Irwin W G. Liquid nitrogen and salicylic/lactic acid paint in the treatment of cutaneous warts in general practice. J R Col Gen Pract 1988; 38: 256-8.
- Focht D R, Spicer C, Fairchok M P. The efficacy of duct tape vs cryotherapy in the treatment of verruca vulgaris. Arch Paed Adolesc Med 2002; 156: 971-4.