CASE #1: Molluscum contagiosum
Molluscum contagiosum (MC) is one of the most common dermatologic conditions encountered by pediatricians and, along with genital warts, among the most prevelant of the STDs. Of all viral infections, MC is perhaps the most protean in its dermatologic incarnations.1
MC is best understood as a follicular process. The condition was named in 1817 for its domed, delled shape (similar to that of a mollusk) and propensity to proliferate. The dell is the center of a follicle, and the rim around the dell is a proliferation of the virally infected cells, which are referred to as molluscum bodies. The histological appearance of these minute ovoid eosinophilic structures is distinctive. Clinically, molluscum bodies can resemble a bacterial or herpetic folliculitis, inflamed cyst, or some type of aberrant sebacous hyperplasia (as seen in this case).2
Two nonviral diseases also carry the appellation molluscum. Skin tags that manifest in pregnancy are referred to as molluscum fibrosum gravidarum, and keratoacantomas—a rapidly proliferating type of squamous cell carcinoma with a benign course—are referred to as keratic or keratotic molluscum, molluscum pseudocarcinomatosus, molluscum sebaceum, and keratinous molluscum.
Mollusca are caused by the molluscum contagiosum virus (MCV), a large, double-stranded DNA poxvirus in the same family as cowpox and smallpox. MCV has no animal reservoir; however there have been a few reports of MC occurring in chickens, sparrows, pigeons, chimpanzees, kangaroos, a dog, and a horse.3 The four subtypes of MC behave in an identical manner clinically. Subtype I (found in 75% to 90% of individuals with MC) and II are common, and subtype III and IV are rare.3
MC is spread through direct contact or by fomites, including any erose scraping tools used on the skin, razors (in particular those used to shave genital areas), bath towels, skin-smoothing utensils, tattoo instruments, and beauty parlor paraphernalia. Communal swimming pools can also be a source of MC.
In adults, the most common source of spread is skin-to-skin contact, likely during a sexual encounter. While many individuals carry MCV — almost 100% of children are exposed to MCV at some point — only 5% to 10% develop lesions of MC.3 The average incubation time of MCV is between two and seven weeks but can be as long as 26 weeks. Researchers have used nonstandardized serum antibodies, complement fixation, fluorescent antibody, tissue-culture neutralization, and agar-gel diffusion techniques to assess MC. Specific MC protein antibodies have been noted in approximately 80% of patients with MC clinically and in about 15% of controls.4
MC manifests as smooth, umbilicated, usually concentric papules that typically measure 1 to 20 mm in diameter. They can be white, flesh-colored, translucent, yellow, pink, or red (especially when irritated). Firm to the touch, MC lacks the gelatinlike consistency of cutaneous cryptococcosis. The central dell or umbilication sits atop a white, waxy, and curdlike core that can be popped out with comedone extractor. This core can be viewed immediately under a microscope in what is known as a crush preparation on a slide with Papanicolaou, Wright, or Giemsa stain. MC can manifest as single lesions, in groups, in plaques, in folliculitis-like patterns, and in pseudo Koebner-type (linear) arrays.
MC can affect any part of the body except for the palms and soles. Distribution in children and adults differ. In children, MC tends to occur on any body area or in areas affected by atopic dermatitis. In immunosuppressed individuals (particularly those with HIV), the face and neck are commonly affected. In the 1980s and 1990s, the prevalence of MCV in patients with HIV was perhaps 20%. With very low CD4 cell counts (i.e., >100 cells/mm3), the prevalence of MC approaches 30% to 40%. In the age of antiretroviral therapy, MC has somehow receded as a dermatosis of HIV.
As a common STD, the distribution of MC is distinct. In immunocompetent adults, the lesions usually appear in the groin beneath the line of the umbilicus and on the genitals and buttocks. If MC is found outside of the underwear/groin area of an adult, consider an HIV test. Such a distribution is likely attributable to some form of intimate contact with another person.
The diagnosis of MC in most cases is clinically obvious. A central dell or umbilication will be present either directly or secondary to freezing the lesions. As in this case, pseudocystic MC, yellow sebaceous hyperplasia type MC, cystic MC, giant MC, pedunculated MC, and MC associated with other cutaneous pathology (especially cysts) can lead to diagnostic uncertainty. Other follicular diseases can coexist with MC, in particular an epidermal inclusion cyst likely secondary to MCV spreading into another disease state that affects the follicle. Commonly, MC occurs secondary to shaving. Advise all patients with MC not to use a razor on the affected area. If absolutely necessary, trim the hair with scissors.
Most cases of MC in immunocompetent adults or children last months and spread contiguously. In children, virtually all cases abate by puberty. Individual papules of MC tend to last for one to two months. MC can recur after its initial clearance in approximately one third of patients, but many develop immunity. It is not clear whether MC’s recrudescence iterates a new infection, an ongoing disease exacerbation, some depression of immunity (as seen in herpes simpex and varicella viruses), or rebound from a quiescent viral state.
MC is a common infection and accounts for approximately 1% of all diagnosed skin diseases.3 A review of the data from the National Disease and Therapeutic Index Survey from 1966 to 1983 shows that the incidence of MC is increasing,5 perhaps attributable to changes in genital shaving practices among men and women.
MC has no systemic manifestations but can evoke an eczematous reaction in 10% of patients, most commonly in children.3 It is unclear whether this reflects an immune phenomenon or a worsening of atophy. It has been noted that eyelid MC can be severe and can include scarring of the peripheral cornea.
In immunocompetent, nonatopic individuals, MC is typically a self-limited disease that does not require treatment.3 When deemed appropriate, multiple local therapeutic options are available for MC.3,6 However, no single intervention has been shown to be convincingly effective in treating MC.3 Lesions can be frozen or popped open with a comedone extractor. Lack of therapeutic success can occur, particularly against the backdrop of immunosuppression. As lesions spread, multiple treatment sessions can be required. Scarring from lesions and treatment is not common.
In this patient, treatment with liquid nitrogen resulted in resolution of the papules.