Molluscum contagiosum is a common cutaneous viral infection caused by the poxvirus Molluscipoxvirus. Structurally, the virus is brick-shaped, contains double-stranded DNA, and is one of the largest viruses known.
PATHOGENESIS AND EPIDEMIOLOGY
Molluscum contagiosum can only replicate in the human epidermis and is spread by skin-to-skin contact, autoinoculation, sexual transmission, and contaminated fomites. Once the infection is localized to the epidermis, it replicates and induces the formation of proliferative skin lesions.
Molluscum can present at any age, but the peak incidence is in children between 0 and 4 years, and the majority of cases are found in those younger than 8 years. Most children presenting with molluscum contagiosum are healthy; however, patients with atopic dermatitis or immunosuppressed individuals tend to have larger, more widespread eruptions. While molluscum can be a sexually transmitted disease, this is more common in adults. Outbreaks have been noted among wrestlers, and there is evidence to support that molluscum is more common in swimmers and children with atopic dermatitis. Molluscum contagiosum infection is usually benign and self-limited, with the disease duration lasting several months to several years.
Molluscum lesions typically begin as 3 to 5 mm or larger in diameter, flat-topped, discrete, dome-shaped, flesh-colored to translucent papules, with a central white core, and they umbilicate as they age (Fig. 312-1). Molluscum lesions commonly occur on the trunk, extremities, and face, but may be generalized as well. Groups of lesions often occur in the body folds and intertriginous areas, secondary to skin-to-skin autoinoculation (see Fig. 312-1). Molluscum contagiosum is usually asymptomatic, although an eczematous, red, scaling patch is commonly observed surrounding the lesions and is termed molluscum dermatitis. Scratching of the dermatitis may spread the virus. Infrequently, molluscum contagiosum may trigger a papular, eczematous, “id reaction,” or a Gianotti-Crosti like reaction, characterized by numerous erythematous and edematous lesions separate from the molluscum lesions.
View of molluscum lesions. A translucent papule with central white area (right side of image), an active inflammatory lesion (bottom left of image), and remnant superficial crusting (upper left corner of image) are visualized.
Molluscum contagiosum is usually diagnosed clinically, based on morphology and distribution. A dermatoscope may assist in visualizing the morphology of the lesions. One may confirm the diagnosis by examining the central core of a molluscum lesion. After appropriate staining, eosinophilic, ovoid, intracytoplasmic inclusions termed molluscum bodies may be observed under the microscope. Small, atypical, and giant lesions may be mistaken for bacterial pustules, verrucae, keratosis pilaris, milia, varicella-zoster, or juvenile xanthogranuloma. These conditions should be considered as a part of the differential diagnosis.