Molluscum Contagiosum

Molluscum contagiosum (MC) is a common, self-limited superficial viral infection of the epidermis predominantly seen in otherwise healthy toddlers and school-aged children.
There has been a drastic increase in prevalence of MC among children in the United States over the last several decades.
MC can also be seen in immunocompromised adults and in sexually active young adults as a sexually transmitted disease. These clinical presentations are discussed in Chapter 17: Mucocutaneous Manifestations of Viral Infections.

MC results from a skin infection with the molluscum contagiosum virus (MCV), a member of the poxvirus family, a large DNA virus.
The virus is spread by skin-to-skin contact or skin to infected fomite contact. Common fomites include wet towels, gym or school equipment, sponges, etc.
Autoinoculation is a common mode of spread in children.
Host factors play a role in acquisition of MC because not all children who have prolonged skin contact with an infected person or item develop MC, and immunocompetent adults also rarely get MC.

MC lesions are dome-shaped, “waxy” or “pearly” appearing, 2- to 8-mm papules with a central white core or umbilication (Figs. 6.9 and 6.10).
Lesions usually appear in clusters or in a linear distribution (autoinoculation) in moist regions of the body such as the axillae, groin, buttocks, posterior thighs, and popliteal fossae.
However, MC can present anywhere on the body as a single lesion or hundreds of lesions.
“Giant molluscum,” representing several smaller lesions clustered into one larger papule, can also be seen.
MC can also become red and inflamed or develop a surrounding eczematous dermatitis, termed “molluscum dermatitis,” both of which herald their spontaneous resolution (Fig. 6.11).
In addition, eczematous id reactions or Gianotti-Crosti syndrome-like reactions (GCLRs) may develop at sites distant from the molluscum (usually on the elbows and knees) and also signals impending resolution of the MC.
The papules of an id or GCLR may resemble molluscum and are often mistaken for a sudden increase in the number of molluscum.
MC is generally asymptomatic, but on occasion may be slightly itchy.
Scratching can result in secondary infection as well as spread via autoinnoculation.
Children with atopic dermatitis are more likely to acquire MC, have a larger number of MC, and more likely to have a prolonged course.

Typical molluscum papules are easily recognized and a biopsy is rarely necessary.
Inspection with a handheld magnifier or dermatoscope often reveals the central core.
A short application of cryotherapy with LN₂ accentuates the central core (Fig. 6.12A,B).

Differential Diagnosis

Flat Warts

Skin-colored to tan, flat-topped verrucous papules, lack central umbilication.

Id (Autoeczematization) Reaction

Itchy, skin-colored to slightly pink, monomorphic, eczematous papules usually located on the extensor elbows and knees occurring in response to a strong inflammatory stimulus.
When present in patients with molluscum, it usually represents an immune-mediated response to molluscum and heralds clearance. Can also occur in response to allergic contact dermatitis or dermatophyte infection (e.g., tinea capitis).

Management

In the majority of children, the course is self-limiting and lesions of MC resolve within 6 to 24 months.
Watchful waiting (for lesions to spontaneously resolve) is often appropriate, especially in children with few lesions who do not have atopic dermatitis.
Patients and parents often seek treatment for several reasons:
1. To help alleviate pruritus and discomfort
2. To prevent further spread on their child or to a sibling or friend
3. Eliminate the associated psychosocial stigma
There is no gold-standard or FDA-approved treatment for molluscum but there are numerous destructive and immunomodulatory methods that are used to induce clearance of MC. The choice of treatment depends on: (1) the age of the patient, (2) the number of lesions present, and (3) location of the lesions.

Management

In Office Treatment

Cantharadin Therapy

Cantharadin, an extract from the blister beetle Cantharis vesicatoria, compounded in a 0.7% or 0.9% solution is a very effective and painless treatment for MC and thus it is often a first-line in-office treatment option for MC in children.
Cantharadin induces blister formation of the epidermis resulting in extrusion of the molluscum viral bodies.
Proper application and patient education are essential for the safe use of cantharadin.
Cantharadin should only be applied in a medical office setting preferably by the physician or other highly trained medical personnel.
A single drop of cantharadin is applied on each MC taking care not to apply on surrounding skin using the blunt wooden end of a cotton-tipped swab or a toothpick.
Parents should be instructed to wash off the cantharadin in 4 to 6 hours (less time if prior treatments resulted in large blister reactions) and to expect blistering or crust formation in 24 to 48 hours.
Cantharadin should be allowed to dry completely before the patient leaves the office. Use of a handheld fan near the area of application is often useful.
Cantharadin should not be applied on the face (especially perioral or periocular sites), in flexures or occluded areas, on mucosal surfaces or on MC with extensive MC dermatitis.
Cantharadin is applied every 3 to 4 weeks, or until lesions resolve.
Parents should be given written instructions that include the time the cantharadin should be washed off, and how to care for blisters and associated pain.
Side effects include large blister formation, pain, pigmentary changes, and scarring.
Currently in the United States, cantharadin is only available for in-office physician use through specialty compounding pharmacies.

Cryotherapy with Liquid Nitrogen (LN₂)

Typically used to treat MC in older children and adults.
For MC, LN₂ is applied with a cotton swab or a Cryogun and frozen lightly for 2 to 5 seconds.
LN₂ works by inducing blister formation allowing for extrusion of the molluscum viral bodies.
Side effects include pigmentary changes, pain, and blister formation.
The associated discomfort is many times not acceptable for young children.

Curettage

Removal of MC with a curette is a definitive treatment option often used in adolescents and adults, with or without use of local anesthesia.
For children amenable to this treatment, the application of lidocaine 4% cream (LMX) or lidocaine/prilocaine cream (EMLA) under occlusion to the areas of molluscum for 30 to 40 minutes prior to curettage can make the procedure painless.

At-Home Treatments

Imiquimod Cream

Works by inducing cutaneous viral mediated immunity.
A thin layer of imiquimod should be applied carefully to each lesion three times daily initially and if not irritating should be used daily.
The main side effect is skin redness and irritation, which is more likely to occur in patients with atopic dermatitis.
Imiquimod is available as a 5% cream (Aldara) or 3.75% cream (Zyclara).

Tretinoin Cream

Presumed to work by inducing local skin irritation and is often used for molluscum on the face.
Tretinoin cream, available in varying concentrations as a cream or gel, is applied nightly to each lesion.
The main side effect is redness, irritation, and an eczematous dermatitis at the site of application.

Oral Cimetidine

Initially found to be effective for the treatment of multiple warts, oral cimetidine can also induce clearance of molluscum by presumably increasing viral-mediated immunity.
For this immunomodulatory effect, a dose of 30 to 40 mg/kg/day in two divided doses is required. The medication is taken until all lesions have resolved.
Cimetidine is most often utilized as an adjunctive treatment for children with numerous MC.

Potassium Hydroxide

Application of twice daily potassium hydroxide 5% to 10% has been reported to be effective in clearing molluscum after several weeks of use.

Other Treatments

A plethora of OTC and over-the-internet products are available and marketed as antimolluscum treatments including salicylic acid, -hydroxy acids, tape stripping, and natural remedies containing plant extracts (MolluscumRx, ZymaDerm, or Emuaid). Their efficacy is variable.

Helpful Hints

Parents of infected children rarely get MC.
Recurrences of MC are rare in immunocompetent persons.
Inflamed MC may become large, pustular, or fluctuant nodules, but the contents are usually sterile.
Although MC are contagious, children should not be quarantined or kept home from school because of MC. The virus may be anywhere and chances are they contracted MC at school!

Points to Remember

In young children with few lesions, aggressive therapy is often not necessary.
MC in healthy, immunocompetent persons is generally self-limiting and resolves spontaneously within 6 to 24 months.
A topical anesthetic such as lidocaine cream, applied under occlusion 1 hour before curettage, local anesthetic injection, or cryosurgery can significantly decrease discomfort.
Redness and inflammation, surrounding eczematous dermatitis, and Gianotti-Crosti-like reactions are signs of immune activation and usually signal impending resolution of molluscum.

SEE PATIENT HANDOUT “Molluscum Contagiosum” IN THE COMPANION eBOOK EDITION.

section name header

Basics ⬇

Pathogenesis ⬆ ⬇

Clinical Manifestations ⬆ ⬇

Diagnosis ⬆