Andrew Tagg. Molluscum contagiosum, Don't Forget the Bubbles, 2017. Available at:
It started as one or two raised little bumps under her arm. They didn’t seem to bother her but as time went on they seemed to increase in number. As a handful became too many to count her parents became concerned. What were these fleshy little lumps? Why wouldn’t they go away? Could they be catching?
What is molluscum contagiosum?
Molluscum is a benign dermatological condition that is exceedingly common in childhood. It is caused by the molluscum contagiosum virus (MCV) – a DNA pox virus – that is distantly related to the human papilloma virus. There are four main subtype (I-IV) with MCV I being the most common. There is an increased incidence in children with atopic dermatitis.
How is it diagnosed?
MCV is a clinical diagnosis based on the classic appearance (see below). There is a validated diagnostic tool that parents can use to help make the diagnosis – the Molluscum Contagiosum Diagnostic Tool for Parents (MCDTP). It has been validated with a sensitivity of 92% and a specificity of 88%.
What do they look like?
They start off as little pimples before slowly growing in size. They are classically described as umbilicated pearls – small creamy raised bumps with a central pit. They can be found anywhere on the body but appear to be more common in the nappy area, in the axilla and on the face and head. This is most likely due to auto-innoculation. Prevalence data suggest that between 5% and 11% of children have been affected.
How is it spread?
MCV is spread by direct contact, usually skin to skin, though it may be transmitted through shared towels or clothing. It is potentially contagious until the last spot has gone. Complete spontaneous resolution may take many months with only 16% of cases resolved after one year.
What are the adverse effects?
Though usually harmless they may cause psychosocial problems in older children with reported incidents of bullying due to the lesions. Increased number of lesions and prolonged duration are more likely to lead to reduced quality of life.
How is it treated?
You can argue that it does not need to be treated as the body’s own immune system will do the job, though this can take some time. Most molluscum pimples clear without scarring. In fact, aggressive treatment is more likely to leave a permanent mark.
Reasons for intervening (from the 2009 Cochrane review):-
- Treating discomfort and itching
- Social stigma/refusal of return to school
- Preventing spread
- Preventing scarring or secondary infection
Traditional remedies rely on irritating the spots thus accelerating the immune response. Once the head of the lesion has been destroyed and the waxy core removed then the virus is destroyed.
Parents can try covering the spots with occlusive tape (think duct tape) for a couple of days before ripping it off, hopefully removing the central core.
This weak solution of aluminium acetate can be dabbed on the spots after washing and allowed to dry.
Once a staple of high school chemistry lessons, this strong alkali has been used to treat the lesions with resolution taking around 30 days or so. The treatment may be discontinued due to pain and irritation on application.
Imiquimod cream induces high levels of interferon-α. Interestingly a couple of large randomized controlled trials have shown that it is not effective though it is often recommended. It’s worthwhile reading this article from JAMA Dermatology (yep, there is such a thing) that goes into why these two trials never saw the light of publication. Both industry funded trials by the drug’s manufacturer showed questionable effectiveness. One, of 323 children aged 2 to 12 years, showed complete clearance at 18 weeks in 24% of the imiquimod group and 26% of the placebo group. The other (379 kids) showed resolution of lesions in 24% of imiquimod treated children and 28% in the placebo group.
Liquid nitrogen, dry ice or similar may be applied to individual lesions. Treatment may need to be repeated and is not well tolerated by young infants.
Pulsed dye laser therapy has been used successfully with minimal scarring but is an expensive treatment for a disease that is usually self limiting.
Romiti, R., Ribeiro, A. P., Grinblat, B. M., Rivitti, E. A. and Romiti, N. (1999), Treatment of Molluscum Contagiosum with Potassium Hydroxide: A Clinical Approach in 35 Children. Pediatric Dermatology, 16: 228–231. doi:10.1046/j.1525-1470.1999.00066.x
Hanna, D., Hatami, A., Powell, J., Marcoux, D., Maari, C., Savard, P., Thibeault, H. and McCuaig, C. (2006), A Prospective Randomized Trial Comparing the Efficacy and Adverse Effects of Four Recognized Treatments of Molluscum Contagiosum in Children. Pediatric Dermatology, 23: 574–579. doi:10.1111/j.1525-1470.2006.00313.x
Olsen JR, Gallacher J, Finlay AY, Piguet V, Francis NA. Time to resolution and effect on quality of life of molluscum contagiosum in children in the UK: a prospective community cohort study. The Lancet Infectious Diseases. 2015 Feb 28;15(2):190-5.
Katz KA. Dermatologists, imiquimod, and treatment of molluscum contagiosum in children: righting wrongs. JAMA dermatology. 2015 Feb 1;151(2):125-6.
Basdag H, Rainer BM, Cohen BA. Molluscum Contagiosum: To Treat or Not to Treat? Experience with 170 Children in an Outpatient Clinic Setting in the Northeastern United States. Pediatric dermatology. 2015 May 1;32(3):353-7.