Clinical Review

Pediatric Molluscum: An Update

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References

Childhood Immunity and Vaccination

Sequence homology between MC133L, a protein of MCV, with vaccinia virus suggests overlapping genes.22 Therefore, it is conceptually possible that the rise in incidence of MCV since the 1980s relates to the loss of herd immunity to variola due to lack of vaccination for smallpox, which has not been offered in the United States since 1972.23 Childhood immunity to MCV varies among studies, but it appears that children do develop antibodies to molluscum in the setting of forming an immune response. Because the rise in molluscum incidence began after the smallpox vaccine was discontinued, the factors appear related; however, the scientific data do not support the theory of a relationship. Mitchell24 has shown that a patient can develop antibodies in response to ground molluscum bodies inoculated into the skin; however, vaccination against molluscum and natural infection do not appear to produce antibodies that would cross-react and protect against other poxviruses, including vaccinia or fowl pox infections.25 Cell-mediated immunity also is required to clear MCV and may account for the inflammatory appearance of lesions as they resolve.26

Demonstrated factors that account for the rise in MCV incidence, aside from alterations in vaccination practices, include spread through sports,9 swimming,11 and AD,7 which have become more commonplace in the United States in the last few decades, supporting the theory that they may be the cause of the increase in childhood MCV infections. Another cause may be the ability of MCV to create factors that stem host immune response.1

Clinical Features

Molluscum lesions have a typical appearance of pearly papules with a central dell. These lesions are lighter to flesh colored and measure 1 to 3 mm.2,4,5 The lesions cluster in the axillae and extremities and average from 10 to 20 per child.6 Lesions clear spontaneously, but new ones will continue to form until immunity is developed. Specific clinical appearances of lesions that are not pearly papules are not infrequent. Table 1 contains a short list of the manifold clinical appearances of molluscum lesions in children.1,2,7,27-35 In particular, certain clinical appearances should be considered. In small children, head and neck lesions resembling milia are not uncommon. Giant or wartlike lesions can appear on the head, neck, or gluteal region in children and are clinical mimics of condyloma or other warts (Figure 1). Giant lesions also can grow in the subcutaneous space and mimic a cyst or abscess.27 Erosive lesions mimicking eczema vaccinatum can be seen (Figure 2), but dermoscopy may demonstrate central dells in some lesions. Other viral processes mimicked include Gianotti Crosti–like lesions (Figure 3) that appear when a papular id reaction forms over the extremities or a localized version in the axilla, mimicking unilateral laterothoracic exanthema.2,36,37 Hypersensitivity reactions are commonly noted with clearance and can be papular or demonstrate swelling and erythema, termed the beginning-of-the-end sign.38

Figure 1. Giant molluscum above the lip of a toddler.

Figure 2. Molluscum with excoriated and erosive lesions clustered and mimicking the appearance of eczema vaccinatum.

Figure 3. Molluscum with dermatitis and small papules mimicking the appearance of an exanthema such as Gianotti Crosti.

Pruritus, erythema, and swelling can occur with clearance but do not appear in all patients. Addressing pruritus is important to prevent disease spread, as patients are likely to inoculate other areas of the skin with virus when they scratch, and lesion number is reduced with dermatitis interventions.36

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