Molluscum contagiosum is a viral infection of human epidermal keratinocytes, caused by a double-stranded DNA virus of the Poxviridae family. Molluscum appears as papules or nodules and sometimes is called "molluscum warts." It is seen most frequently in HIV-uninfected children (up to 5% of children in the United States), in sexually active young adults, and in immunocompromised persons. It occurs in 5-18% of HIV-infected persons. Molluscum is benign but may cause extensive and cosmetically bothersome lesions, particularly in persons with advanced HIV infection.
Transmission occurs by person-to-person skin-to-skin contact (e.g., sexual activity, contact sports [especially wrestling], or simply touching) or via fomites (towels, bedclothes, clothing [including underwear], soft toys, shaving utensils, electrolysis equipment, tattooing tools, and sponges). The virus may be spread to other areas via self-inoculation (e.g., scratching, shaving, or touching a lesion).
In immunocompetent persons, the infection usually resolves spontaneously after 6-12 months, though genital lesions may remain longer. In HIV-infected persons, the lesions may be more extensive and persistent. There is a strong correlation between the degree of immunosuppression and the risk of molluscum infection, the number of lesions, and the ability of lesions to resist treatment.
Patients complain of new papules on the trunk, axillae, antecubital and popliteal fossae, face, or genital/crural area. Papules of molluscum contagiosum may cause no symptoms but also can be intensely pruritic or tender to the touch. Ask patients whether others in the home (especially children and adolescents) or their sex partners have similar papules. Genital lesions are transmitted sexually; patients may recall seeing such lesions on the genitals of a previous partner.
Ask about fever or other systemic symptoms to evaluate for other causes of the papules.
Perform a thorough evaluation of the skin, genitals, and mouth. Molluscum commonly presents as multiple grouped lesions. The lesions are white, pink, or flesh colored; shiny, smooth surfaced, firm, pearly, and spherical (dome-shaped) papules (2-5 mm) or nodules (6-10 mm), with umbilicated, or dimpled, centers. Patients with HIV infection may develop giant lesions (>1 cm) or clusters of hundreds of small lesions. Occasionally, molluscum will have a polyp-like appearance. Lesions are usually found on the head, face, or neck or in the genital area, but may affect every part of the body except the palms and soles. Molluscum may occur inside the mouth, vagina, and rectum, and around the eyes. Lesions on the eyelids can cause conjunctivitis.
A partial differential diagnosis includes the following:
- Disseminated cryptococcosis
- Histoplasmosis skin lesions
- Penicillium marneffei
- Other fungal skin lesions
- Syphilis, condyloma acuminata, vulvar syringoma for multiple small molluscum genital lesions
- Squamous or basal cell carcinoma
The diagnosis of molluscum usually is based on the characteristic appearance of the lesions. Perform histologic or other laboratory testing to confirm the diagnosis or to exclude other infections or malignancies. Special staining will show keratinocytes containing eosinophilic cytoplasmic inclusion bodies. Electron microscopy will show poxvirus particles.
Because molluscum does not cause illness and rarely causes symptoms, the treatment usually is undertaken primarily for cosmetic purposes. For individuals with large or extensive lesions, molluscum may be disfiguring or stigmatizing, and treatment may be important for their well-being. Treatment (particularly of genital lesions) can be considered in order to prevent transmission to others.
In HIV-infected patients, molluscum is difficult to eradicate and lesions often recur, particularly if immune suppression persists. Effective antiretroviral therapy may achieve resolution of lesions or significant improvement in the extent or appearance of molluscum and should be recommended for all.
Lesions that remain after weeks of antiretroviral therapy should be treated to prevent further spread. Refer complex cases to a dermatologist.
Choice of treatment modality is based on age, likelihood of compliance, number and size of lesions, and potential adverse effects of treatment. Therapeutic options include the following:
- Local excision: May be done by curettage, cryotherapy, electrocautery, or evisceration. Adverse effects include pain, irritation, soreness, and mild scarring. Repeated treatments are necessary. Curettage appears to be most efficacious (even for children) but is painful and requires anesthesia and a large time commitment over the course of several visits; it also has a risk of scarring. Relapse is common.
- Imiquimod 5% (Aldara): An immune response modifier; stimulates production of interferon-alfa and other proinflammatory cytokines, inducing a tissue reaction associated with viral clearance from the skin. Apply TIW for up to 16 weeks or QPM for 4 weeks. Clearing can take up to 3 months. Limited studies; painless.
- Podophyllotoxin: Can be administered by a health care provider and washed off after 1-4 hours. This treatment is caustic, may cause significant irritation, and has limited effectiveness. It is contraindicated for use during pregnancy. Patient-administered podophyllotoxin (Podofilox) may be a safer alternative to podophyllum. Adverse effects include burning, pain, inflammation, erosion, and itching.
- Cantharidin 0.7%: Can be applied by a health care provider. One study of 300 children found that lesions cleared after two visits. This treatment may cause allergic reactions, stinging, and blistering. Do not use cantharidin around the eyes.
- Tretinoin (Retin-A) 0.1% cream: Can be applied to lesions BID. Adverse effects include drying, peeling, irritation, and soreness.
- Trichloroacetic acid: Can be administered by a health care provider. Controlling the depth of acid penetration is difficult. Adverse effects include pain and irritation; mild scarring is common.
- A combination of salicylic and lactic acid: Response is highly variable and recurrence is common.
- Laser therapy: Safe, efficient, tolerable, and efficacious.
- Cidofovir 1-3% topical cream: Applied BID for 2 weeks, followed by a 30-day rest period and then two additional cycles. This treatment has been shown to be effective in several small studies and case reports, but it is expensive and difficult to compound. No systemic adverse effects are noted.
- Silver nitrate paste: May be used to burn each lesion individually.
- Molluscum infection is benign but may be distressing.
- Molluscum infection may be transmitted both sexually and nonsexually, through direct contact with lesions. Molluscum also can be transmitted indirectly by contact with infected objects.
- Latex condoms or barriers may not prevent transmission of genital molluscum.
- To prevent the spread of molluscum, instruct patients to take the following precautions:
- Avoid close contact between their molluscum lesions and the skin, mouth, and genitals of other people.
- Avoid picking at, squeezing, or puncturing the lesions, as a lesion's central plug is full of viral particles that can be spread easily by coming into contact with other parts of the body. In addition, lesions may become secondarily infected.
- Wash hands frequently.
- Keep fingernails short.
- Avoid shaving in areas with lesions because shaving could result in lesions spreading to other areas.
- Avoid sharing towels, bedclothes, clothing, shaving utensils, bathing equipment, or other objects that have been in contact with molluscum lesions.
- Wash all contaminated items in very hot, but not scalding, water.
- Cover lesions with clothing, if possible.
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