By Ellen S. Haddock, MBA, and Lawrence F. Eichenfield, MD
Molluscum
Molluscum typically presents as smooth, flesh-colored, flat-topped papules 2-8 mm in diameter with central whitish area, which is composed of the causative molluscum pox virus. While central depressions called umbilications are common, they may not be present in early molluscum lesions.1,2 Lesions most often occur on the trunk and arms, but can occur anywhere.3-5 Individuals usually have multiple lesions, which may be clustered especially in areas of skin-to-skin contact.5,6 Molluscum lesions can be itchy.
Molluscum is a benign viral skin infection caused by the molluscum contagiosum virus, which is a member of the poxvirus family. Molluscum infections are common, affecting 5%-11% of children.5,7 Molluscum most often affects children younger than 8-years-old,5 with an average age of 5.8 years.8 The infection is spread through skin-to-skin contact with other individuals and by autoinoculation, which means that the infection can be spread from one area of an individual's skin to another when he or she scratches a lesion and then touches another area. It also can be spread by contact with fomites like towels and sponges.1 An association between public swimming pool use and molluscum infection has been reported, but this may have more to do with shared towels and equipment like kick-boards than transmission through the water itself.9 Molluscum sometimes is spread through contact sports like wrestling6 and between children sharing a bath.9 In adults, in whom molluscum is much less common because of acquired immunity,10 molluscum may be sexually transmitted or associated with HIV; however, this is rarely the case in children.1
Children with atopic dermatitis have increased risk of molluscum infection in part because breaks in their skin and pruritus facilitate autoinoculation through scratching.11 Not uncommonly, molluscum lesions become inflamed, with tenderness, erythema, and crust. In a study by Berger et al., 22% of patients had inflamed molluscum lesions.3 The appearance of inflamed molluscum lesions may raise concern about bacterial infection, but more often, the inflammation is a sign that the immune system is reacting to the viral infection and has almost "won the battle."10 After inflamed molluscum lesions develop, the total number of molluscum lesions typically declines,3 and some consider inflamed molluscum lesions to be a "beginning of the end sign," indicating that the infection may soon resolve.10 If the child is afebrile, lesions are itchy and painless, skin culture is negative, and there is no lymphangitis or spreading erythema, the inflammation is more likely a sign of impending resolution than bacterial secondary infection, and the urge to prescribe antibiotics should be resisted.10
As seen in this case, some patients with molluscum (5%) develop a diffuse, monomorphous, papular, or papulovesicular eruption that is an id reaction.3 This may appear to be eczema-like, lichenoid in appearance, or mimicking Gianotti-Crosti syndrome (papular acrodermatitis of childhood).3 It typically affects the arms and legs, is bilateral, and may be pruritic. The id reaction may occur in conjunction with inflamed molluscum, as is true in this case. The diffuse eruption can sometimes be mistaken for a sudden increase in the number of molluscum lesions, but the papular dermatitis lesions do not have the flat-topped dome-shape nor white centers.3 On average, the id reaction lasts about 6 weeks, after which both it and the primary molluscum lesions typically resolve.3 Although not seen in this case, more than a third of molluscum patients develop a pruritic, erythematous, eczematous area around molluscum lesions, termed molluscum dermatitis or eczema molluscatum, which may be more prominent than the molluscum itself.3 The eczematous patch typically surrounds molluscum lesions but also may occur at distant sites.12 This reaction is especially common in patients with atopic dermatitis, 51% of whom develop it.3 It is considered a hypersensitivity reaction and may be asymptomatic or minimally pruritic.12 Molluscum dermatitis suggests that the immune system has taken notice of the infection and is fighting it13; however, it does not necessarily indicate impending resolution.3
Differential diagnosis
The differential diagnosis for molluscum includes herpes simplex, warts, and milia.14 Like molluscum, herpes simplex lesions can have central umbilication, but the lesions are vesicular rather than solid. Warts typically have a rough, jagged surface in contrast to the smooth surface of molluscum lesions. Milia tend to be smaller and not flat topped. They are more common in infants and adults than in children and primarily affect the face.
Inflamed molluscum lesions and molluscum dermatitis can be mistaken for atopic dermatitis, and molluscum-associated id reactions may exacerbate atopic dermatitis. Inflamed molluscum and molluscum with id reaction could be confused with scabies, which may become crusted and also may be accompanied by id reaction. Presence of serpiginous linear burrows would suggest scabies rather than molluscum, and the diagnosis of scabies can be confirmed by scraping a burrow and looking for a mite or its feces under a microscope.