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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.
Molluscum contagiosum, the viral skin infection, is best left alone to heal by itself rather than being treated with medication, destructive treatments or creams. When comparing imiquimod (a skin cream that activates the immune system) with nothing, about 40% of people were clinically clear by 6 months in either group. Treatment increased the chance of severe adverse events such as irritation and scarring fourfold.
The majority of other treatment comparisons were from studies judged by the authors to be of low quality. Based on the findings from this study, clinicians should advise people who have a healthy immune system to leave molluscum contagiosum to clear by itself.
Considering the limited evidence on their effectiveness and risk of scarring even treatment for cosmetic reasons has uncertain evidence. Parents should be warned of the possibility of pain resulting from treatment of children.
Why was this study needed?
Molluscum contagiosum is a viral skin infection and transmission occurs by close personal contact or via contaminated surfaces. The exact prevalence is unknown as many people do not seek medical attention but in a 2005 UK general practice-based survey of patient records, the annual incidence of new cases was 261 per 100,000 patients and 80% of cases are in children under 15.
It is generally a harmless condition that gets better within a few months without specific treatment but rarely, it can spread around the body and take up to 18 months or more to clear completely.
Treatment is often sought for cosmetic and social reasons or to prevent spread, however, the scientific basis for treatment is unclear and practitioners may be unsure whether to recommend treatment or not. The current study aimed to evaluate treatment options to see what worked if anything.
What did this study do?
This study reviewed 22 randomised controlled trials involving 1,650 participants - mostly children - with molluscum contagiosum. The trials compared 20 topical treatments (applied to the skin) and two oral treatments with either an alternative treatment or placebo in people who were not immunocompromised. Follow-up ranged from three to 28 weeks after randomisation. Only five studies had follow-up longer than three months.
The main outcome was a short-term clinical cure (up to three months after treatment start), shown by complete clearance of lesions.
Quality of evidence overall was judged to be low as most studies had small sample sizes and many had a high drop-out rate. The control comparison group was often an alternative treatment rather than a placebo, which may have shown some treatment effect which makes the overall effectiveness difficult to judge.
What did it find?
For 5% imiquimod cream compared to placebo:
- Moderate-quality evidence showed a lack of effect for clinical cure either in the short-term (relative risk [RR] 1.33, 95% confidence interval [CI] 0.92 to 1.95; 4 studies, 850 participants), medium-term (RR 0.88, 95% CI 0.67 to 1.14; 2 studies, 702 participants) or long-term (RR 0.97, 95% CI 0.79 to 1.17; 2 studies, 702 participants). High-quality evidence showed no difference in short-term improvements (RR 1.14, 95% CI 0.89 to 1.47, 4 studies, 850 participants). The clearance at six months was about 40% in either group.
- Moderate-quality evidence showed application site reactions were more frequent (RR 1.41, 95% confidence interval [CI] 1.13 to 1.77), including severe application site reactions (RR 4.33, 95% CI 1.16 to 16.19).
There were 11 comparisons between different treatments with evidence considered low quality. Two of these found:
- Compared to cryospray, tetrafluoroethane that freezes the tissue, 5% imiquimod was less effective (RR 0.60, 95% CI 0.46 to 0.78; 1 study, 74 participants).
- Compared to 10% potassium hydroxide, 5% imiquimod was also less effective (RR 0.65, 95% CI 0.46 to 0.93; 2 studies, 67 participants).
- Other comparisons finding one treatment more effective than another tended to be based on studies with a small number of participants and with wide confidence intervals reducing the reliability of the evidence.
- It is possible that some treatments are more effective than placebo but the quality of the evidence is too poor to make any recommendation.
What does current guidance say on this issue?
The British Association of Dermatologists in 2015 suggest that many treatments are painful and it is often better not to treat as the spots will go away by themselves. They further add that it is almost always best not to treat children, especially if it will cause pain.
What are the implications?
Unless new evidence emerges for the benefit of one treatment over another, molluscum contagiosum should be left to heal naturally. One topical treatment (5% imiquimod) was no more effective than a placebo and had more severe adverse effects.
However, there was insufficient evidence to assess the effectiveness of other treatments currently recommended such as curettage (applying anaesthetic and scraping off the spots) or cryotherapy using liquid nitrogen.
If more studies are conducted, it would be useful to measure recurrence rates, the spread of the disease to other people, disease-related quality of life and scarring as these were not well reported in the existing evidence.
Citation and Funding
van der Wouden JC, van der Sande R, Kruithof EJ, et al. Interventions for cutaneous molluscum contagiosum. Cochrane Database Syst Rev. 2017;5:CD004767.
Bibliography
NHS Choices. Molluscum contagiosum. London: Department of Health; 2017.
NICE CKS. Molluscum contagiosum. Scenario: Management of molluscum contagiosum. London: National Institute for Health and Care Excellence Clinical Knowledge Summaries; 2012.
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