Description of the condition
Molluscum contagiosum is a viral skin infection most frequently encountered in children. The infection is caused by the molluscum contagiosum virus (MCV), which is classified within the family of poxviruses (Poxviridae). Infection follows contact with infected people or contaminated objects. Molluscum contagiosum usually presents as single or multiple (usually no more than 20) painless, spherical, shiny, pearly white papules that classically have a central dimple. Their size may vary from tiny 1 mm papules to large nodules over 1 cm in diameter (Rogers 1998). The lesions may itch.
As well as the common form of benign skin tumours (mostly found in children), there is also a sexually transmitted variant of molluscum contagiosum which occurs on genital, perineal, pubic, and surrounding skin. Molluscum contagiosum lesions may also appear in or around the mouth (Whitaker 1991). Molluscum contagiosum has also been observed with other diseases in people with a damaged immune system (Gottlieb 1994). People with HIV infection are particularly prone to molluscum contagiosum and prevalence in this population may be as high as 5% to 18% (Matis 1987; Hira 1988; Husak 1997). The focus of this review will be the common form of molluscum contagiosum only.
Molluscum contagiosum occurs worldwide but is much more frequent in certain geographic areas with warm climates, like Fiji, Congo, and Papua New Guinea. Infection is rare in children under the age of one year, and typically occurs in the two to five year old age group (Rogers 1998). The age of peak incidence is reported as being between the ages of 2 and 3 years in Fiji (Postlethwaite 1967), and between 1 and 4 years in the Congo (formerly Zaire) (Torfs 1959). In Papua New Guinea the annual attack rate for children under 10 years of age was 6% (Sturt 1971). For developed countries, population-based occurrence rates are scarce. In a large questionnaire study among parents of children attending kindergartens and elementary schools the reported prevalence of molluscum contagiosum was 5.6% and 7.4% respectively (Niizeki 1984). Much higher prevalence rates have been reported during outbreaks in closed communities (Overfield 1966).
In the United States, from 1990 to 1999 the estimated number of physician visits for molluscum contagiosum was 280,000 per year (Molino 2004). One out of 6 Dutch children aged 15 years have visited their doctor for molluscum contagiosum at least once (Koning 1994). There is generally no difference in incidence between males and females (Sturt 1971; Relyveld 1988; Koning 1994). However, an unequal sex ratio was found in studies from Japan (Niizeki 1984), Alaska (Overfield 1966), and Fiji (Hawley 1970), where boys were affected more often. This is probably due to habits associated with the spread of the infection, such as swimming (Postlethwaite 1967; Niizeki 1984). Outbreaks may occur among children who bathe or swim together. A history of eczema was found in 62% of children with molluscum contagiosum in Australia (Braue 2005). In the adolescent and adult age groups sexual transmission becomes important.
The estimated incubation period varies from 14 days to 6 months. Lesions enlarge slowly and may reach a diameter of 5 to 10 mm in 6 to 12 weeks (Sterling 1998). After trauma (for example, scratching), or spontaneously after several months, inflammatory changes result in the production of white fluid, crusting, and eventual destruction of the lesions. However, new lesions tend to appear as the old ones resolve as a consequence of the virus spreading to other areas of skin. The duration both of the individual lesion and of the entire episode is highly variable. Crops of molluscum may appear to come and go for several months, and although most cases are self limiting and resolve within six to nine months, some may persist for more than three or four years. Follow-up studies (Liveing 1878; Hawley 1970) confirm these figures and show that individual lesions are unlikely to persist for more than two months.
A Japanese study described spontaneous resolution on average 6.5 months after infection in 205 out of 217 children (94.5%) affected by molluscum contagiosum (Takemura 1983). One month after the first consultation with the dermatologist, 23% of the children were cured.
Particularly in atopic people (who are prone to asthma, hay fever, or eczema), there is a tendency for a patch of eczema (which is often particularly itchy) to develop around one or more of the lesions a month or more after their onset (De Oreo 1956; Beaulieu 2000). Erythema annulare centrifugum (a widespread rash of red inflammatory rings) has also been reported (Vasily 1978). Chronic conjunctivitis and superficial punctate keratitis may similarly complicate lesions on or near the eyelids (Haellmigk 1966; Redmond 2004). The eczema and conjunctivitis subside spontaneously when the molluscum lesion is removed.
Molluscum contagiosum behaves differently in HIV-infected individuals. As immunodeficiency progresses, molluscum contagiosum becomes more common and resistance to therapy increases. Frequently, multiple lesions in atypical areas such as the face and neck can be found. Only limited data are available on the course of the disease in this group of people.
Description of the intervention
Molluscum contagiosum is a self limiting disease in people with an uncompromised immune system. Therapy is not necessary for recovery and awaiting spontaneous resolution is an important management strategy. Most lesions resolve within months without scarring in otherwise healthy people (Ordoukhanian 1997). Treatment is intended to accelerate this process. Destruction of the lesions and the production of an inflammatory response (Sterling 1998) are means by which resolution of the lesions could be hastened.
Reasons to treat molluscum contagiosum include:
(a) alleviating discomfort, including itching;
(c) social stigma associated with many visible lesions;
(d) limiting its spread to other areas of the body and to other people;
(e) preventing scarring and secondary infection; and
(f) preventing trauma and bleeding of lesions.
A large number of treatment options are used for molluscum contagiosum. These can be divided into three major categories:
(a) physical destruction of the lesions;
(b) topical agents (i.e. those applied directly to the lesions); and
(c) systemic treatment (i.e. those affecting the whole body).
Physical destruction has been recommended as the preferred method for treatment of molluscum contagiosum by many authors. Dermatology textbooks mention removal of the lesion with a sharp curette or the application of liquid nitrogen (cryotherapy) as being simple, painless, and usually effective treatments (Sterling 1998; Lowy 1999). Gentle squeezing or pricking with a sterile needle (Berger 1996) are alternative recommended destructive therapies. Most of these therapies will have to be repeated at three to four weekly intervals. Treatment may be painful and may result in scarring (Friedman 1987). Squeezing of lesions may even lead to the formation of large abscesses due to the disruption of virus into the deeper layer of the skin (dermis) (Brandrup 1989).
Topical preparations such as podophyllotoxin, liquefied phenol, tretinoin, cantharidin, or potassium hydroxide can be used to produce a local inflammatory response. In children, prior application of local anaesthetic cream may reduce the pain of treatment involving physical destruction or local inflammation (Rosdahl 1988; de Waard 1990), although severe side-effects have been reported in a case of excessive application of lidocaine-prilocaine (Wieringa 2006). Other proposed topical treatments include immune response modifiers such as imiquimod and cidofovir.
Systemic treatment with cimetidine has been suggested as a possible treatment because of its systemic immunomodulatory effects; it increases lymphocyte proliferation and inhibits suppressor T-cell function (Orlow 1993; Sterling 1998).
Little data are available with regard to prevailing practice. In the US, paediatric dermatologists seem to favour cantharidin, imiquimod, and pulsed dye laser, taking into account the age of the child, number and location of lesions, and input of the parents (Arbuckle, personal communication). This is different from general practice in the Netherlands, where waiting for natural resolution and physical destruction are the most popular options.
Why it is important to do this review
Molluscum contagiosum is a common reason for consultation in family practice and dermatology. There are many treatment options available, some of which are painful and some may leave scars. A decision may be made in favour of active therapy to prevent further spread, relieve symptoms, prevent scarring, and for cosmetic and social reasons. Indeed, many parents are concerned about the stigma associated with the lesions. Children with molluscum may be excluded from attending nursery and from participating in physical activities such as swimming. However, the scientific basis for treatment is unclear. Consequently, many practitioners find themselves in a dilemma as to whether or not to promote active treatment and, if they do decide on an active treatment strategy, are unclear as to the best option. We have carried out this systematic review to evaluate treatment options for molluscum contagiosum.