Clinical Overview

Molluscum contagiosum is a chronic viral infection caused by molluscum contagiosum virus (MCV), a large double-stranded DNA poxvirus belonging to the genus Molluscipoxvirus. The condition presents with characteristic pearly, dome-shaped papules with central umbilication, typically measuring 2-5 mm in diameter. MCV is highly contagious through direct skin contact, fomites, and sexual contact, making it a common infection in children aged 2-10 years and in sexually active adults. The disease is self-limiting but requires treatment to prevent spread and reduce cosmetic morbidity.

Epidemiology

Molluscum contagiosum affects approximately 2-3% of the global pediatric population, with higher prevalence in tropical and subtropical regions. In temperate climates, incidence peaks during autumn and winter months, suggesting respiratory viral transmission patterns. Adult infections account for 5-18% of all molluscum cases, predominantly transmitted sexually with associations to immunosuppression. HIV-positive patients with CD4 counts below 100 cells/μL experience significantly higher infection rates (5-18% compared to 0.3% in immunocompetent adults). Geographic variations show higher prevalence in atopic dermatitis populations due to compromised skin barrier function. The average duration of untreated molluscum contagiosum ranges from 6-9 months in immunocompetent individuals to 2-5 years in immunocompromised patients.

Pathophysiology

MCV replicates exclusively in the cytoplasm of infected keratinocytes using viral DNA-dependent RNA polymerase. The virus encodes immunomodulatory proteins including MCV-encoded interleukin-18 binding protein (MCV-IL-18BP), which suppresses interferon-gamma production and delays cell-mediated immune response. This immune evasion mechanism explains the chronic nature of molluscum infections. The characteristic central umbilication represents a crater-like depression filled with caseous material containing viral particles and infected cell debris. Histopathologically, molluscum lesions demonstrate keratinocyte hyperplasia with distinctive eosinophilic molluscum bodies (Henderson-Patterson bodies) in the cytoplasm, pathognomonic for the disease.

Clinical Presentation

Molluscum contagiosum typically begins with solitary lesions that gradually increase in number over weeks to months, with typical presentations showing 10-50 lesions though counts exceeding 100 are documented in immunocompromised patients. Individual papules are 2-5 mm, pearly white to skin-colored, dome-shaped with characteristic central umbilication that may contain yellow-white caseous material. Common sites include face, trunk, and intertriginous areas in children, with genitals being predominant in sexually transmitted disease. Secondary bacterial infection occurs in 10-15% of cases due to scratching and skin trauma. Associated dermatitis develops in 30-50% of patients, manifesting as erythema and excoriation surrounding lesions (molluscum dermatitis).

Diagnosis

Clinical diagnosis is typically straightforward based on morphology and distribution; characteristic pearly papules with central umbilication are pathognomonic. Dermoscopy reveals central dell (umbilication) with surrounding yellowish-white material. Histopathology shows stratified squamous epithelium with cytoplasmic molluscum bodies (Henderson-Patterson bodies) that are intracytoplasmic and eosinophilic. Electron microscopy can identify viral particles if diagnosis is uncertain. Differential diagnosis includes comedones, follicular papules, varicella, herpes simplex, and sebaceous cysts. Dermoscopic examination helps distinguish molluscum from comedones (which lack central dell) and other infectious agents.

Treatment Algorithm

Observation: For asymptomatic, uninfected lesions in immunocompetent children, observation is reasonable given self-limited nature over 6-12 months. However, most parents prefer treatment to reduce transmission risk. Observation carries risk of viral spread to other sites and contacts.

Topical Therapy: Imiquimod 5% cream (Aldara), a toll-like receptor 7 agonist, applied 3 times weekly for 12-16 weeks achieves clearance in 60-80% of immunocompetent patients and 30-50% of HIV-positive patients. Response takes 8-12 weeks. Tretinoin 0.05-0.1% applied nightly for 8-12 weeks shows 50-70% clearance rates with improved efficacy when combined with destructive methods. Potassium hydroxide 15-20% solution applied twice daily causes chemical destruction of lesional tissue with 60% resolution in 2-3 months. Cantharidin 0.7% (Cantharone) applied by clinician, left 4-6 hours then washed off, causes blistering and destruction in 60-75% at first application, with repeated applications monthly as needed.

Destructive Procedures: Cryotherapy with liquid nitrogen applied for 10-15 seconds causes immediate freeze-thaw cycle with recurrence rates of 5-10% per lesion if single treatment. Multiple treatments spaced 2-4 weeks apart optimize clearance. Curettage with a dermal curette or comedone extractor under topical anesthesia (lidocaine 5% cream) mechanically removes lesional material with 85-95% clearance at single treatment but higher recurrence (15-20%) if incomplete removal. Laser therapy using pulsed dye laser (585-595 nm) or CO2 laser provides rapid destruction with minimal scarring in 2-3 sessions. Electrocautery under topical anesthesia provides immediate removal with 90% clearance rates.

Systemic Therapy: For extensive disease or immunocompromised patients, systemic cidofovir (150 mg/kg intravenous injection) has demonstrated efficacy in HIV patients with CD4 <100 cells/μL, though parenteral administration limits use. Oral antivirals (acyclovir, valacyclovir) show limited efficacy as MCV is not significantly sensitive to these agents. Combination therapy of imiquimod 5% cream with cryotherapy or curettage achieves higher clearance rates (75-85%) than monotherapy in immunocompetent patients.

Prognosis

Molluscum contagiosum is self-limited in immunocompetent hosts, with 90% of lesions involuting within 6-12 months of onset. However, individual lesions persist an average of 2-4 months even with treatment. Secondary bacterial infections may prolong course and worsen cosmetic outcomes. Recurrences are uncommon (5-10%) following complete clearance in immunocompetent patients. Immunocompromised patients (HIV with CD4 <100 cells/μL) experience progressive disease with hundreds of lesions and duration exceeding 2-5 years without immune reconstitution. Post-inflammatory hyperpigmentation or hypopigmentation develops in 10-15% of treated cases, particularly in dark-skinned individuals. Scarring is rare with appropriate treatment techniques, occurring in <5% of cases managed with destructive procedures.

When to See a Dermatologist

Consult a dermatologist if lesions are widespread (>50 lesions), involve sensitive areas (genitals, face), show signs of secondary bacterial infection, or are refractory to initial topical therapy. Immunocompromised patients should seek specialist evaluation for optimal management and consideration of systemic therapy. Atopic dermatitis patients with concurrent molluscum benefit from specialist management given higher complication rates.

Frequently Asked Questions

Q: Is molluscum contagiosum sexually transmitted in adults?
A: Yes, in adults molluscum contagiosum is predominantly sexually transmitted through direct genital contact. Lesions in the genitals, thighs, and lower abdomen suggest sexual transmission. The virus can survive on fomites for several hours, so transmission through shared clothing or bedding is possible. Sexual partners should be examined and treated if infected.

Q: How long does treatment typically take?
A: Most topical treatments require 8-16 weeks of consistent application for optimal results. Destructive procedures like cryotherapy or curettage may require multiple sessions spaced 2-4 weeks apart for complete clearance. Some patients achieve resolution in 4-6 weeks with aggressive combination therapy, while others require 12-20 weeks. Patience is essential as individual lesions take 2-4 months to respond even with treatment.

Q: Will my child get molluscum contagiosum again after treatment?
A: Reinfection is uncommon (5-10%) in immunocompetent children following complete clearance. However, if skin barrier is compromised (atopic dermatitis, eczema), infection risk increases. Good hygiene practices including regular handwashing, avoiding skin-to-skin contact during active infection, and treating concurrent atopic dermatitis reduce reinfection risk significantly.

Q: Should my child stay home from school with molluscum?
A: Most schools don't require exclusion for molluscum contagiosum if lesions can be covered with clothing or bandages. The CDC recommends covering visible lesions to reduce transmission. Consider keeping children home if lesions are on exposed areas, or covering lesions with waterproof dressings during activities involving close contact or communal bathing.

References

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