The dearth of evidence regarding treatments for non-genital molluscum contagiosum leaves physicians uncertain if any interventions work better than allowing the infection to resolve itself.
"The overall conclusions have hardly changed. We found no strong evidence either for or against the most commonly used treatment options for molluscum contagiosum. Allowing for natural resolution of the infection remains a reasonable approach," wrote van der Wouden JC, et al. in a review summarized in JAMA Dermatology online on Dec. 27.
"We found some evidence to suggest that 10% potassium hydroxide is more effective than saline; 5% solution of potassium hydroxide is favored compared to 2.5% solution of potassium hydroxide; 10% povidone iodine solution plus 50% salicylic acid plaster is favored compared to salicylic acid plaster alone; and homeopathic calcarea carbonica is favored compared to placebo," the authors wrote.
In patients without immune deficiency, resolution of molluscum contagiosum can take several months, or in extreme cases, 3-4 years. However, patients may desire treatment for social or cosmetic reasons, or to avoid scratching or spreading the infection, wrote the authors who were led by Johannes C. van der Wouden, M.D., of the Amsterdam Public Health Research Institute in Amsterdam.
Updating a 2009 review, the authors searched the Cochrane Skin Group Specialized Register, Central, Medline, Lilacs and Embase through July 2016. They also searched six trial registries, scoured the included studies for additional relevant references and queried pharmaceutical companies and experts to identify further relevant randomized controlled trials (RCTs). This search identified 11 new studies, making an evaluable pool of 22 studies with a total of 1,650 participants.
Among the 11 new studies were four never-published RCTs of imiquimod, which collectively provided moderate-quality evidence for lack of effect of 5% imiquimod compared to placebo in the short-, medium- and long-term. Pooling results of the four unpublished studies with a total of 544 patients and treatment times between eight and 16 weeks showed a clinical cure rate of 14.5% (79 patients) for imiquimod, versus 11.8% (36 patients) for placebo (pooled risk difference: 4%; 95% CI: -1%-8%).
Researchers found similar but more certain results for short-term improvement (four studies, 850 participants, 12 weeks after starting treatment, risk ratio/RR 1.14 (95% CI: 0.89-1.47; high-quality evidence). The same 4 studies showed that after 12 weeks, RR for complete clearance was 1.33 (95% confidence interval/CI: 0.92-1.93). At 28 weeks, 2 studies with 702 subjects showed RR of complete clearance was 0.97 (95% CI: 0.79-1.17).
"We can provide no reliable evidence-based recommendations for the treatment of molluscum contagiosum at present, except for 5% imiquimod, which based on moderate-quality evidence from three unpublished studies is probably no more effective in terms of clinical cure than its vehicle but is probably more harmful in terms of application-site reactions," the authors wrote.
High-quality evidence from three studies with 827 participants showed RR of 0.97 for topical imiquimod versus vehicle, but pooled RR for application-site reactions in imiquimod-treated cohorts was 1.41 (95% CI 1.13-1.77).
Based on the high-quality evidence, the authors said that topical 5% imiquimod is no more effective than its vehicle in providing short-term improvement. Likewise, long-term clinical cure rates were 38.3% for imiquimod versus 39.7% for placebo (pooled risk difference, 1%; 95% CI = -9%-6%).
The remaining publications reviewed involved small trials that pitted one therapy against another, often without a placebo comparator. Authors found limited, low-quality evidence from 11 comparisons for short-term cure efficacy of treatments including cryospray and potassium compared to imiquimod, of benzoyl peroxide 10% compared to 0.05% tretinoin, and of tea tree oil plus iodine versus tea tree oil or iodine alone, to name a few examples.
van der Wouden et al. wrote that the small studies reporting no differences might have produced clinically relevant differences if treatments were evaluated in larger samples. The authors also could not guarantee that they did not miss relevant research clinical trials, one relevant study was ongoing at the time of publication, and authors were still attempting to classify and evaluate several others.
van der Wouden JC, van der Sande R, et al. “Interventions for cutaneous molluscum contagiosum,” Cochrane Database System Review. 2017 May 17, 2017.
van der Wouden JC, Koning S, Katz KA. “Interventions for nongenital molluscum contagiosum in persons without immune deficiency,” JAMA Dermatology. Dec 27, 2017. DOI: 10.1001/jamadermatol.2017.5118.