In a blog for a non-medical audience, Lynda Ware, Senior Fellow in General Practice with Cochrane UK, looks at the latest evidence on treatments for cutaneous molluscum contagiosum, a common skin infection.
Despite sounding like a spell straight out of Harry Potter, molluscum contagiosum is a skin infection caused by a virus called molluscum contagiosum virus (MCV). It is common and can affect any age group, although children are more often affected than adults.
What do the spots look like?
MCV causes raised, dome-shaped spots, usually 2-6mm across, although they can be as large as 2cm. They have a shiny surface and a central dimple and are usually skin-coloured. The spots often occur in clusters and MC spots can appear on any part of the body, sparing only the palms and soles of the feet. They are usually readily diagnosed by their appearance and no tests are needed.
How do we catch molluscum contagiosum virus?
MCV is highly contagious, in other words it is spread from person to person by touching affected skin. It can also be transmitted by clothes, towels, toys etc which have been in contact with the virus. The virus can also be spread by scratching or picking at the spots. Molluscum contagiosum is more common and often more extensive in people with atopic eczema and people whose immune system is suppressed, for example by HIV infection or immunosuppressant medication, may develop large numbers of spots.
What problems can molluscum contagiosum virus cause?
The infection most commonly resolves over time but it can be doggedly persistent. On the whole, the spots clear within 6-18 months but they can last for several years. If the spots are extensive and/or highly visible they can cause significant psychological distress because of their cosmetic appearance. The spots sometimes heal leaving a scar, especially if they have been traumatised or become infected. They do not usually cause symptoms unless inflamed or infected when they can become painful or itchy. If traumatised the spots may bleed slightly.
How can molluscum contagiosum be treated?
When I was a newly qualified GP (35 years ago…oh dear) one popular treatment was to poke out the centre of the spot with an orange stick. This aimed to remove the central core, which harboured the virus. Treatments listed in the 2012 NICE CKS (Clinical Knowledge Summaries) for the management of molluscum contagiosum include the following recommendations :
- Treatment is not usually recommended. If lesions are troublesome or considered unsightly, use simple trauma or cryotherapy, depending on the parents’ wishes and the child’s age:
- Squeezing (with fingernails) or piercing (orange stick) lesions may be tried, following a bath. Treatment should be limited to a few lesions at one time.
- Cryotherapy may be used in older children or adults, if the healthcare professional is experienced in the procedure.
This advice is based on pragmatism and expert opinion.
- The following treatments may be considered by a specialist:
- Surgical (e.g. curettage, cautery).
- Topical (e.g. pulsed dye laser, phenol ablation, imiquimod 5%, cantharidin, potassium hydroxide 10%, podophyllin, silver nitrate paste, benzoyl peroxide 10%, and retinoids).
This advice is based on what CKS considers to be good clinical practice in UK.
Let’s take a look at what the Cochrane Review has to say
In May 2017 the Cochrane systematic review Interventions for cutaneous molluscum contagiosum was published. The review authors aimed to assess the effectiveness of various treatment and management strategies for cutaneous (ie on the skin, but excluding the genital areas) molluscum contagiosum in people whose immunity was not compromised.
Cochrane reviews are periodically updated and there were 11 new studies to add since the previous version, making 22 in total, involving 1650 participants. 20 of these studies looked at topical treatments and two looked at systemic treatments. Most of the participants were children or young adults.The review considered clinical cure in the short, medium and long term, as well as short term improvement and adverse effects.
Three of the studies included were unpublished (2005) and had been undertaken by 3M Pharmaceuticals, and submitted to the American Food and Drug Association. Together with another published trial, these studies contributed nearly half of the participants (about 800 in all) and compared 5% imiquimod cream to placebo (a dummy cream).
The other studies considered a variety of comparisons of treatment including cryospray (this is a freezing treatment), 10% Australian lemon myrtle oil, 10% benzoyl peroxide, 0.05% tretinoin, 5% sodium nitrite, 5% salicylic acid, tea tree oil and several others. The quality of evidence for comparisons of these treatments was low (in other words the findings may be true but are likely to change with more clinical data.) There were no randomised trials for several commonly used treatments such as expressing (poking!) lesions with an orange stick or topical hydrogen peroxide.
The authors concluded that:
‘No single intervention has been shown to be convincingly effective in the treatment of molluscum contagiosum.’
With particular reference to 5% imiquimod cream, there was moderate quality evidence (in other words this is probably true, but further trial data could change the conclusions) that 5% imiquimod cream is no more effective than placebo in terms of cure, but leads to more local skin reactions where it has been applied. There was high quality evidence (in other words we can be very certain that the conclusions are true) that 5% imiquimod is not better than placebo in bringing about short term improvement.
So what should we do?
No one treatment emerges triumphant from this Cochrane review. In the majority of cases natural resolution is the way forward. Explanations about how long it may take to resolve, as well as reassurance that there is usually nothing to worry about, will help encourage patience. Trying to prevent spread to others by not sharing towels etc also makes sense but exclusion from sport, school and social gatherings is not necessary. Advice about resisting the urge to pick or scratch the spots will help prevent further spread.
So, unfortunately, there is no magic wand (or, perhaps that should be orange stick….)
Lynda Ware has nothing to disclose.
References may be found here.