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Freezing warts

The other issue concerning warts is their treatment, which occupies a great deal of time for patients, GPs and dermatologists. Two papers from the department of Dermatology at Leicester Royal Infirmary have addressed the effectiveness of different treatment cryotherapy strategies in randomised controlled trials. In patients who do not respond to conservative therapy, like use of keratolytic compounds, cryotherapy with liquid nitrogen is often used. It is also offered by many GPs. The two issues addressed in these papers are the value of a second freeze-thaw cycle, and the interval between cryotherapy treatments. Can cure rates be affected by different cryotherapy regimens?

Value of a second freeze-thaw cycle

The first study examined this point [1]. It was a randomised, open study of 300 patients of all ages newly referred for treatment of warts of hands or feet. Daily wart paint use by patients was part of the treatment.

Study

Patients were seen at 3-weekly intervals. Plantar warts were pared with a scalpel until capillary bleeding. Patients were randomised to receive single or double freezing. Cryotherapy involved applying liquid nitrogen using cotton wool buds until a halo of ice was seen around each wart. For those receiving the double freezing technique, all signs of freezing were allowed to resolve before repeating the procedure. At 3 months, cure rates were assessed. A cure was defined as no visible evidence of warts at review, or those who had returned a postal questionnaire saying their warts were cured.

Results

Results were available on all but 35 of the 300 patients. On an intention to treat basis, reporting results as a percentage of all patients randomised, single freeze produced a three month cure rate of 38% (56/149) and double freeze 45% (68/151; no significant difference).
When hand warts and plantar warts were analysed separately, a slightly different picture emerged. Cure rates for hand warts was not improved by double freezing (45% cure compared with 41% cure for single freeze). Plantar warts had a 50% cure with double freezing, compared with only 29% using the single freeze technique. This was statistically significant (relative risk 1.7, 95% CI 1.1 - 2.8).

NNT

The NNT was 4.8 (95% CI 2.6 - 26); this means that for every five patients with plantar warts treated with double freezing, one more will have a three month cure who would not have been cured if treated with a single freezing technique.

Frequency of freezing

The traditional frequency of cryotherapy when treating warts is 3 weeks. The second Leicester study investigated whether increasing the frequency of cryotherapy to 2 weeks or 1 week had any influence on the cure rate.

Study

Newly referred patients were asked if they were prepared to attend clinic weekly if necessary. Those who agreed were randomised to receive cryotherapy at 1, 2 or 3 weeks. Wart paint was to be used daily during the duration of the study. Cryotherapy and plantar wart preparation were the same as the first study. Blistering or soreness was noted at each visit, and blistered warts were not re-treated. Inflamed or painful warts were treated, subject to patient tolerance. Cure rate was assessed after 3 months of treatment, and after receiving 12 treatments (3 months for weekly group, 6 months for 2-weekly group and 9 months for the 3-weekly group).

Results

Warts cleared faster with more frequent treatment. The mean time to clearance was 6 weeks for weekly, 10 weeks for 2-weekly and 15 weeks for 3-weekly treatment. The mean number of treatments to achieve clearance was the same - 5.
The cure rate was the same (about 45%) after 12 treatments, but after three months higher cure rates were seen with more frequent treatments.

NNT

Weekly, rather than 3-weekly, treatment produced significantly higher cure rates (relative risk 1.7, 95%CI 1.1 - 2.7). The NNT was 5.8 (95% CI 3.1 - 41); this means that for every six patients with warts treated with cryotherapy weekly, one more will have a three month cure who would not have been cured if treated every three weeks.

Adverse events

Adverse events are given in the table.
Adverse events with cryotherapy for warts
Event weekly 2-weekly 3-weekly
soreness 7% 5% 3%
blistering 2% 7% 0%
withdrawn with pain 1% 2% 0%
Blistering was significantly more common in those treated weekly. The number needed to harm (NNH) was 3.5 (2.5 - 5.4); this means that for every four patients with warts treated with cryotherapy weekly, one more would have a blister who would not have had one if treated every three weeks.

Workload

More frequent treatment means more work. The mean number of treatments given for weekly treatment was 9 (range 1 - 29). It was greater than that for those treated 2-weekly (6, range 1 - 21) and 3-weekly (6; range 1 - 20).

Comment

These were well conducted studies on large numbers. They probably represent the truth for cryotherapy treatments of warts. Bandolier has chosen to present the results as intention to treat, as did they. This is the most conservative way of presenting the data. So what we can say is that double-freezing of plantar warts is effective, and that more frequent freezing of all warts leads to a quicker cure, but not a greater rate of cure.

References:

  1. J Berth-Jones, J Bourke, H Eglitis et al. Value of a second freeze-thaw cycle in cryotherapy of common warts. British Journal of Dermatology 1994 131:883-6.
  2. J Bourke, J Berth-Jones, PE Hutchinson. Cryotherapy of common viral warts at intervals of 1, 2 and 3 weeks. British Journal of Dermatology 1995 132:433-6.



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