Molluscum contagiosum

Molluscum warts; Mollusca contagiosa

Common, self-limited viral infection of the epidermis caused by the molluscum contagiosum virus (MCV) from the Poxviridae family. It primarily affects preschool- and school-aged children; clustered, extensive, or persistent courses are seen in atopic dermatitis and in immunosuppression.

MCV infections occur worldwide, with higher prevalence in warm, humid climates and in community settings. Peak incidence is in childhood, approximately between 2 and 10 years of age. In adults, lesions are more often localized to the genital area or occur in the context of immunosuppression. Atopic dermatitis is considered a major risk factor for extensive disease.

MCV is divided into four genotypes:

• MCV type 1 (most common type, especially in children)

• MCV type 2 (more common in adults and immunosuppressed patients)

• MCV types 3 and 4 (rare)
  

MCV infects exclusively epidermal keratinocytes and induces lobular epidermal hyperplasia with characteristic intracytoplasmic inclusion bodies. The virus evades the innate and adaptive immune response through various immune evasion mechanisms, which explains its often prolonged persistence.

Transmission:

• Direct skin contact with infected lesions

• Autoinoculation through scratching, rubbing, or shaving

• Contaminated objects (fomites: towels, washcloths, sports equipment)

• Sexual transmission in adults with genital lesions
  

Predisposing factors:

• Incubation period usually several weeks to months (approximately 2–7 weeks, occasionally longer)

• Atopic skin promotes dissemination and perilesional eczematization

• Immunosuppression (HIV, transplantation, biologics) promotes extensive and atypical courses
  

Typically, 1–5 mm skin-colored, whitish, or pink, smooth, shiny, dome-shaped papules with a characteristic central dell (umbilication) are present. They are often multiple, grouped, or arranged linearly due to autoinoculation.

Key features:

• Monomorphic, broad-based papules with a waxy surface

• Centrally expressible, whitish, crumbly, infectious content

• Usually asymptomatic; occasional pruritus
  

Clinical practice:

• Perilesional eczema (molluscum dermatitis) is common, especially in atopic patients

• Inflammatory erythema and swelling of individual lesions may be part of the spontaneous immune reaction and regression — not automatically a sign of bacterial superinfection

• In immunosuppression: lesions may be larger (>5 mm, so-called “giant molluscum”), more numerous, and atypically configured
  

The diagnosis is usually clinical and does not require further ancillary testing.

Typical clinical criteria:

• Monomorphic, centrally umbilicated, dome-shaped papules

• Smooth, waxy surface

• Grouping or linear arrangement due to autoinoculation

• Expressible whitish content
  

Dermoscopy (helpful in diagnostic uncertainty):

• Central white-yellowish amorphous structures (“white core”)

• Peripheral vascular loops or crown vessels
  

Biopsy/histology: Indicated only in cases of diagnostic uncertainty, atypical course, or suspicion of a differential diagnosis.

Pitfalls — further evaluation in:

• Solitary lesion in adults (DD: basal cell carcinoma, keratoacanthoma)

• Very large, ulcerated, or treatment-resistant lesions

• Extensive involvement without known immunosuppression

• Genital lesions with atypical appearance (DD: condylomata acuminata)

• Suspected opportunistic infection in immunosuppressed patients (DD: cryptococcosis)
  

Preferred sites in children:

• Face, neck

• Axillae, flexures

• Trunk, extremities
  

More common in adults:

• Lower abdomen, inner thighs, genital region (sexually transmitted)

• Extensive distribution in immunosuppression
  

Palms and soles are typically not affected.

• Slowly increasing, small umbilicated papules over weeks to months

• Contact with affected children or household members

• Spread of new lesions after scratching, shaving, or friction

• Known atopic dermatitis

• In adults with genital lesions: possible sexual transmission

• In very numerous, large, atypical, or treatment-resistant lesions: indication of possible immunosuppression (ask about HIV status and immunosuppressive medication)
  

Lobular epidermal hyperplasia with an endophytic growth pattern. Characteristic findings are large intracytoplasmic inclusion bodies in keratinocytes — the so-called Henderson-Patterson bodies (also molluscum bodies). These arise through accumulation of viral particles and displace the nucleus to the periphery. An inflammatory dermal reaction with lymphocytic infiltrate may occur in the surrounding tissue, especially during spontaneous regression or superinfection.

• Autoinoculation with increase in lesion number

• Molluscum dermatitis (perilesional eczema), especially in atopic patients

• Secondary bacterial superinfection

• Postinflammatory hypo- or hyperpigmentation

• Scarring, especially after manipulation or aggressive destructive therapy

• Psychosocial burden due to cosmetic impairment

• In immunosuppression: extensive, persistent, or atypical course with therapeutic challenges
  

• Avoid scratching and squeezing the lesions

• Use personal towels, washcloths, and razors; do not share them

• Treat concomitant eczema consistently to reduce autoinoculation

• Cover manipulated or inflamed lesions whenever possible

• In genital lesions, address sexual transmission and recommend condoms

• A general exclusion from school, daycare, or swimming pools is usually not necessary and is not evidence-based
  

In immunocompetent children, molluscum lesions usually heal spontaneously, but often only after months; courses lasting 12–18 months or longer are possible. Complete spontaneous remission is the rule. In pronounced atopic dermatitis and in immunosuppression, persistent, disseminated, or recurrent courses are more likely. Scars arise mainly from manipulation or aggressive therapy, not from the infection itself.

Principle

The treatment decision depends on age, number and location of lesions, degree of distress, eczematization, transmission risk in the environment, and immune status. In immunocompetent children with few asymptomatic lesions, a watchful waiting approach is often appropriate. Patients should be informed about the self-limited nature of the condition, but also about the potentially long time to resolution.

Mechanical and destructive procedures (first-line options)

• Curettage: Effective with immediate results; often painful in children — local anesthesia with lidocaine/prilocaine cream (EMLA cream) is recommended

• Cryotherapy: Effective; painful, with risk of blistering, hypopigmentation, and scarring, especially in darker skin types

• Cantharidin (available in some countries): Topical application by the physician; effective, well tolerated in children, but not approved everywhere
  

Topical options (alternatives)

• Potassium hydroxide (KOH) 5–10%: Topical self-application possible; note irritant potential, application instructions required

• Tretinoin cream: Possible alternative, especially in widespread involvement; irritant potential

• Imiquimod 5%: Not recommended as routine treatment; Cochrane analysis shows no consistent benefit over placebo in uncomplicated disease; may be considered in selected cases

Intralesional immunotherapy (escalation)

• Intralesional injection of antigens (e.g., Candida antigen, MMR vaccine): Increasingly described, especially for multiple or treatment-resistant lesions; evidence is still limited, but promising
  

Special situations

• Genital lesions in adults: Inform sexual partners; curettage or cryotherapy preferred; consider STI screening

• Immunosuppressed patients: Extensive courses may require optimization of the underlying disease/immunosuppression; systemic antiviral therapy (e.g., cidofovir) has been described in individual cases of severe immunodeficiency, but without robust controlled evidence

• Molluscum dermatitis: First use topical corticosteroids to treat the eczema; destructive treatment of the molluscum lesions only after eczema control
  

Pitfalls

• Avoid aggressive therapy in toddlers with few lesions — the risk of scarring often outweighs the benefit

• Do not use imiquimod as standard therapy

• Do not mistake the inflammatory regression phase for superinfection and avoid unnecessary antibiotics
  

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