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Is Duct Tape Occlusion Therapy as Effective as Cryotherapy for the Treatment of the Common Wart?
Arch Pediatr Adolesc Med. 2002;156:975-977.
THIS RANDOMIZED controlled trial was conducted to assess whether duct
tape occlusion therapy is as effective as cryotherapy for the treatment of
common warts.1 Patients 3 to 22 years of age
who visited the pediatric clinics on a military base in Washington State with
at least 1 common wart on an extremity were approached for study enrollment.
Sixty-one subjects were enrolled and randomized to either cryotherapy or duct
tape occlusion therapy.
The cryotherapy group had liquid nitrogen applied to the study wart
every 2 to 3 weeks for a maximum of 6 treatments or until wart resolution.
The duct tape occlusion group had a small piece of duct tape applied to the
study wart, which was left in place for 6 days. This tape was removed on the
evening of the sixth day and then replaced the following morning for a maximum
of 2 months or until wart resolution. Subjects were instructed to return to
the clinic for evaluation every 2 to 3 weeks in the cryotherapy group and
every 4 weeks in the duct tape group. Prior to the administration of therapy,
each patient had his or her study wart measured with calipers at every clinic
visit. Patients who did not follow up at the clinic were contacted by telephone
to determine whether their warts had resolved. Ten of the 61 patients who
had enrolled in the study were lost to follow-up. At the study's conclusion,
a greater proportion of patients in the duct tape group than in the cryotherapy
group had complete resolution of their study wart (84.6% vs 60.0%, respectively; P = .05). The investigators concluded that duct tape occlusion
therapy is significantly more effective than cryotherapy for the treatment
of common warts.
We analyzed this study according to the guidelines provided by the Users' Guide to the Medical Literature2
published by the American Medical Association. In this analysis, we evaluate
the validity of the results, the size and precision of the treatment effect,
and the applicability of these results to patient care.
RANDOMIZATION OF SUBJECTS
We asked the following questions: (1) Were patients randomized? (2)
Was randomization concealed? (3) Were patients analyzed in the groups to which
they were randomized? (4) Were patients in the treatment and control groups
similar with respect to known prognostic variables? This study was a randomized,
controlled, noninferiority trial. Patients were randomized by a computer-generated
code. We assume that randomization was concealed using this method. Although
not explicitly stated, we also assume that the outcomes for all patients with
complete follow-up were analyzed within their original randomization group.
The patients in the 2 treatment groups were similar with respect to sex, age,
baseline size of warts, and wart location. As this was a randomized trial,
additional unmeasured factors that might have had prognostic significance
should be equally distributed between the study groups.
BLINDED ASSESSMENT
We asked the following questions: (1) Were patients aware of group allocation?
(2) Were clinicians aware of group allocation? (3) Were outcome assessors
aware of group allocation? Given the nature of the 2 therapies, the investigators
could not blind the subjects to group allocation. The study personnel were
initially blinded to the treatment groups, as the duct tape was removed before
each clinic visit, and both groups were instructed to debride their warts
similarly before visiting the clinic. At each visit, study nurses measured
and recorded each wart size before determining an individual subject's treatment
group and administering the appropriate therapy. While this protocol was designed
to maintain the blinding of the outcome assessors, it is possible that having
the study nurses both assess the outcomes and administer therapy may have
resulted in unblinding of the study personnel over time. However, the caliper
measurements should have provided a relatively objective, quantitative measurement
of wart sizes.
More importantly, patients who did not follow-up in the clinic were
contacted by telephone to report their treatment responses to study personnel.
More subjects in the duct tape group reported their outcomes by telephone.
Because the subjects were not blinded to their treatment, their qualitative
assessment of wart resolution may have been biased. However, because there
was no placebo group and because both treatment groups in this study received
treatment, it is unclear in which direction any bias due to the unblinding
of parents might go. One might expect it to favor the more conventional treatment,
which is, in this case, cryotherapy.
FOLLOW-UP
Follow-up was completed for 51 (84%) of the 61 enrolled subjects. Six
patients from the cryotherapy group and 4 patients from the duct tape group
were lost to follow-up. The authors did not report when or why these subjects
were lost to follow-up. Similarly, the authors did not report patients' adherence
to the study protocol. As we will discuss in the following section, the loss
of 16% of the patients to follow-up has important implications for interpreting
the results of this study.
TREATMENT EFFECT SIZE AND PRECISION
The investigators reported the statistically significant benefit of
duct tape occlusion therapy over cryotherapy. Specifically, 85% of patients
treated with duct tape and 60% of patients treated with cryotherapy had resolution
of their study wart. The reported P value of .05
implies that we can state with 95.2% confidence that these results were not
due to chance alone. However, the study did not report the 95% confidence
interval (CI), which is the more clinically relevant measure of treatment
effect. The 95% CI is calculated using a standard equation based on the number
of patients randomized to each treatment group and their outcomes.3 We calculated that the 95% CI for this study's reported
treatment effect is 1.1 to 48.1, and we can state with 95% confidence that
the true treatment effect is somewhere between these 2 values. In other words,
while this study found a treatment effect of 24.6%, the true treatment effect
may be as small as 1.1% or as large as 48.1%. While both the P value and the 95% CI indicate that the observed difference between
the 2 groups is statistically significant at the  = .05 level, the
95% CI provides a measure of the clinical significance of this difference
by defining the range of potential treatment effect.
Because 16% of the patients in the trial were lost to follow-up, it
is also important to consider the effect that this missing data could have
on the study's results. The magnitude of effect that patient loss to follow-up
may have had on this study can be determined by including that 16% of patients
in the treatment effect analyses using a range of hypothetical outcomes. The
worst-case scenario would be if, at the conclusion of this study, the 6 cryotherapy
patients lost to follow-up had wart resolution and the 4 duct tape patients
lost to follow-up had residual wart. By adding these 10 worst-case outcomes
to the 51 known outcomes, we calculated that wart resolution would have occurred
in 73% of patients in the duct tape group and 68% of patients in the cryotherapy
group (95% CI, -17 to 28). This 95% CI includes zero, indicating that
the 5% difference between the 2 treatment groups is not statistically significant.
Therefore, if we take into account the effect that the patients lost to follow-up
might have on the results of the study, duct tape therapy would be no more
effective than cryotherapy. However, this is a maximally conservative estimate.
GENERALIZABILITY
The study population included patients 3 to 22 years of age with at
least 1 common wart located on an extremity who visited the pediatric and
adolescent clinics at the Madigan Army Medical Center in Washington State.
While this is a unique population presenting to a single center, these results
are likely generalizable to most patients receiving treatment at pediatric
primary care clinics in other settings. However, the authors did not mention
other factors that affect warts' response to therapy, including the duration
that the study wart had been present and the patients' prior use of wart removal
therapies other than cryotherapy.4 Therefore,
it is unclear whether the results of this study may also be applied to patients
with any of these clinical characteristics.
CLINICALLY IMPORTANT OUTCOMES
The study's primary outcome was resolution of the study wart 2 months
after initiation of treatment. Adverse outcomes were not specifically quantified,
but they were reported to be more frequent and more severe in the cryotherapy
group.
Ideally, a study of wart therapy should be long enough to adequately
assess both wart resolution and recurrence. The Cochrane review of treatments
for cutaneous warts suggests that subjects should be followed up for 6 months
to assess cure more completely.4 The 2-month
follow-up in this study may have affected its ability to detect these important
clinical outcomes. Although the authors stated that they did not intend to
measure wart recurrence, this is nevertheless a clinically important outcome
with important implications for treatment efficacy. In 1 prior study,5 the cure rate of cryotherapy decreased by 26% when
study wart presence was reassessed 19 months after initiation of therapy.
There are additional clinically important outcomes that were not assessed
in this study. The authors had initially intended to measure the duration
to cure as a secondary outcome, but they were not able to do so as a result
of erratic patient follow-up. Owing to the small number of patients enrolled
in the study, the authors did not compare the response of study warts by their
anatomic location.
TREATMENT BENEFITS AND COSTS
There are many potential practical advantages of duct tape treatment
over cryotherapy. Duct tape treatment is easily performed at home and seems
to be well-tolerated. In addition, it may be more cost-effective than cryotherapy,
as duct tape is relatively inexpensive and therapy would not require multiple
clinic visits.
CONCLUSIONS
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This study has important implications. As the authors conclude, duct
tape therapy may be more effective than cryotherapy for the treatment of common
warts. However, given the percentage of patients lost to follow-up, we calculate
that it is possible that there is no difference in treatment effect between
the 2 therapies.
Although primary care physicians frequently use cryotherapy for wart
removal, a recent Cochrane review that assessed the efficacy of local treatments
for cutaneous, nongenital warts found inconclusive evidence to support the
efficacy of cryotherapy for this indication.4
The 2 small trials that have compared cryotherapy with placebo failed to demonstrate
an advantage of cryotherapy over placebo and were classified by the Cochrane
reviewers as low-quality. According to this review, the best available evidence
supports the use of topical treatments that contain salicylic acid. Such preparations
have been shown to have a modest, but significant, treatment benefit over
placebo. However, the 2 trials that have compared the efficacy of cryotherapy
with that of topical salicylic acid and/or lactic acid found no significant
difference between the treatment groups. In addition, when considering medical
therapy for the common wart, it is also important to consider their rate of
spontaneous resolution. One large survey of institutionalized children found
that 66% of warts spontaneously resolved within 2 years.6
Further studies comparing the efficacy of duct tape therapy with that
of both placebo and salicylic acid are indicated. In the meantime, pediatricians
may consider presenting duct tape as a therapeutic option to patients with
extremity warts who, after discussing the risks and benefits of the various
treatment options with their physician (including the option to not treat),
request a non–salicylic acid therapy.
AUTHOR INFORMATION
Corresponding author: Dimitri A. Christakis MD, MPH, Department of
Pediatrics, Child Health Institute, University of Washington, 146 N Canal
St, Suite 300, Seattle, WA 98103.
Sarah Ringold, MD;
Jason A. Mendoza, MD;
Beth A. Tarini, MD;
Colin Sox, MD
Seattle, Wash
REFERENCES
1. Focht III DR, Spicer C, Fairchok MP. The efficacy of duct tape vs cryotherapy in the treatment of verruca
vulgaris (the common wart). Arch Pediatr Adolesc Med. 2002;156:971-974.
FREE FULL TEXT
2. Guyatt G, ed, Rennie D, ed. Users' Guide to the Medical Literature: A Manual
for Evidence-Based Clinical Practice. Chicago, Ill: American Medical Association; 2002.
3. Sackett DL, Straus SE, Richardson WS, Rosenberg W, Haynes RB. Evidence-Based Medicine: How to Practice and Teach
EBM. 2nd ed. Edinburgh, Scotland: Harcourt; 2000:233-243.
4. Gibbs S, Harvey I, Sterling JC, Stark R. Local Treatments for Cutaneous Warts. In: The Cochrane Library [database on CD-ROM]. Oxford, England: Update
Software; 2002. Updated quarterly.
5. Keefe M, Dick DC. Cryotherapy of hand warts: a questionnaire survey of "consumers.". Clin Exp Dermatol. 1990;15:260-263.
PUBMED
6. Massing AM, Epstein WL. Natural history of warts. Arch Dermatol. 1963;87:306-310.
SECTION EDITORS: DIMITRI A. CHRISTAKIS, MD, MPH; HAROLD P. LEHMANN,
MD, PhD
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