As its name implies, molluscum contagiosum is a highly contagious viral infection that has little morbidity. This infection is most commonly encountered in children. The diagnosis is made on clinical grounds after inspection of the characteristic skin findings. When seen in the genital region of adults, molluscum contagiosum is considered to be a sexually transmitted disease. This infection rarely occurs in immunocompetent adults outside sexual transmission. In adults with no clear evidence of transmission, an evaluation for an immunosuppressed state should be undertaken. Patients taking chronic immunosuppressive medications and those with the acquired immunodeficiency syndrome are more prone to infection with molluscum contagiosum.
Clinical Findings: Young children are often affected by this common viral infection. Children pass the virus from one to another through close contact. The incubation period is 2 to 4 weeks. The characteristic finding is of small (3-5 mm), dome-shaped papules with a central dell. The coloration can be pink to slightly whitish. Solitary lesions may be appreciated, but clusters of lesions are often encountered. They may appear on any part of the body. Slight pruritus may accompany the lesions, but otherwise there are no symptoms. Molluscum lesions have a tendency to become inflamed. When this occurs, they can become tender. Inflamed lesions are bright red and can bleed if the child scratches or traumatizes them. The more inflamed a lesion becomes, the more likely it is to leave scarring. Scarring can also occur if the lesion becomes secondarily infected. Most noninflamed lesions spontaneously resolve within 6 months.
Young and older adults who present with molluscum contagiosum in the genital region are believed to have acquired the infection through sexual contact. The number of lesions in these cases tends to be increased, and the lesions tend to be localized to the groin. These also spontaneously resolve over time with no therapy. Immunosuppressed individuals, especially those with human immunodeficiency virus (HIV) infection, have a high incidence of molluscum contagiosum viral infections. These infections tend to be widespread and can be larger than the typical version acquired in childhood.
Pathogenesis: Molluscum contagiosum is caused by an enveloped, large, double-stranded DNA poxvirus, of which there are four unique types. Humans are the only known species to be infected by this virus. The virus has been designated molluscum contagiosum virus (MCV), and the four types MCV1 through MCV4. The virus is spread by close physical contact, and trans- mission on fomites has also been established. The virus attaches to the glycosaminoglycans on the surface of the targeted cell. The viral DNA gains entry into the cell cytoplasm, where it replicates itself. The virus carries with it a viral RNA polymerase, which acts to transcribe the viral genes, as well as a viral DNA polymerase for replication of its DNA. Early and late proteins are produced. The early proteins are generally for viral replication, and the late proteins are for production of the structural shell of the virus. These processes all occur within the cytoplasm of the infected cell. Once the virus has replicated, the infected cell typically dies, and the brick-shaped viral particles are released.
Histology: Skin biopsies of molluscum contagiosum are very characteristic, and the infection is easily diagnosed histologically. However, biopsies usually are not obtained because the disease is diagnosed clinically. The virally infected cells have molluscum bodies. The molluscum bodies change from small, eosinophilic cytoplasmic bodies in the stratum basalis into larger basophilic bodies in the outer epidermis. As they enlarge, they often compress the nucleus of the infected cell. These intracytoplasmic inclusion bodies have been termed Henderson-Patterson bodies.
Treatment: Often in children, a watch-and-wait approach is the best therapy, because most cases resolve spontaneously. Many destructive methods are available. Liquid nitrogen cryotherapy is highly effective, but most children have difficulty tolerating the pain it can cause. Many other therapies have been used, including tretinoin cream, salicylic acid, curette, cantharidin, and imiquimod. Patients who are immunosuppressed can be treated with any of these modalities. Attempts to decrease immunosuppressive medications should be coordinated through the patient’s transplant surgeon or primary care physician. Patients with widespread molluscum contagiosum and coexisting HIV infection have benefited from highly active antiretroviral therapy (HAART).