Molluscum Contagiosum

Detailed Overview

The condition is highly contagious and spreads via direct skin-to-skin contact, fomites (such as towels or pool equipment), and autoinoculation. While the lesions are typically asymptomatic and resolve spontaneously over months to years in immunocompetent individuals, they can cause distress, pruritus, and cosmetic concern. In adults, presentation in the anogenital region is considered a sexually transmitted infection. Severe, widespread, or giant lesions should prompt investigation for underlying immunodeficiency, particularly HIV.

Epidemiology & Demographics

Highly prevalent worldwide, especially in warm, humid climates. Peak incidence occurs in children aged 1 to 10 years. An estimated 2-8% of children worldwide are affected. In adults, it is a common STI.

Etiological Mechanism

Caused by the Molluscum contagiosum virus (MCV), a DNA poxvirus. There are four major subtypes (MCV 1-4), with MCV-1 being the most common cause in children and MCV-2 more often associated with sexual transmission in adults.

Primary Causes

Direct skin-to-skin contact with an infected individual

Fomite transmission (sharing towels, clothing, sponges)

Sexual contact (in adults)

• Atopic Dermatitis: Disrupted skin barrier increases susceptibility to autoinoculation and widespread infection.
• Immunosuppression: Patients with HIV/AIDS (CD4 count < 100 cells/µL) or those on immunosuppressants can develop severe, intractable disease.
• Swimming pools/bathhouses: Increased risk of exposure via shared fomites.

The MCV infects the epidermal cells, specifically the stratum basale, replicating in the cytoplasm (characteristic of poxviruses). As the virus replicates, the epidermal cells hypertrophy and proliferate, forming a lobulated mass. Large intracytoplasmic inclusion bodies (Henderson-Patterson bodies) form, which eventually push the host cell nucleus to the periphery. The resulting cellular destruction and accumulation of viral particles form the central umbilication and the characteristic cheesy core of the lesion.

Characteristic Clinical Presentation

• Painless bumps: Patients note the appearance of small (2-5 mm) papules on the skin.
• Pruritus: Itching may occur, especially if accompanied by an eczematous reaction (molluscum dermatitis).

Physical Examination Signs

• Firm, dome-shaped, flesh-colored or pearly papules with central umbilication.
• Common locations: trunk, axillae, antecubital/popliteal fossae in children; groin/genitals in adults.
• BOTE sign (Beginning Of The End): Lesions may become inflamed, erythematous, and swollen just prior to spontaneous resolution.

• Secondary bacterial infection: Due to scratching, most commonly by Staphylococcus aureus.
• Molluscum dermatitis: Eczematous reaction surrounding the lesions.
• Scarring: May occur spontaneously or post-treatment (e.g., cryotherapy).

Diagnostic Criteria & Guidelines

Diagnosis is overwhelmingly clinical, based on the characteristic appearance of firm, umbilicated papules. Dermoscopy can aid by showing a central polylobular white-to-yellow amorphous structure with peripheral crown vessels.

Differential Diagnosis

• Warts (Verruca vulgaris)
• Chickenpox (Varicella)
• Cryptococcosis (in HIV patients)
• Basal Cell Carcinoma (single giant molluscum)

Laboratory Tests & Biomarkers

• Histopathology (if biopsied): Epidermal hyperplasia with large eosinophilic intracytoplasmic inclusion bodies (Henderson-Patterson bodies).
• HIV testing: Indicated in adults with widespread, facial, or giant lesions.

• Incubation
  2 to 6 weeks (up to 6 months) after exposure.
• Eruptive
  Appearance and spread of characteristic papules.
• Inflammatory
  Host immune response triggers inflammation (BOTE sign), leading to resolution.

Second-Line & Adjunctive Therapy

Topical retinoids (Tretinoin 0.025% cream applied once daily at night) or Imiquimod 5% cream (applied 3x weekly) can be considered, though efficacy is variable. Curettage is highly effective but painful and may leave scars. Recently FDA-approved Berdazimer 10.3% topical gel is an option for patients >1 year old.

Surgical & Procedural Management

Curettage or physical extraction of the central core can provide rapid resolution but requires local anesthesia (e.g., EMLA cream) and carries a risk of scarring.

Recommended Lifestyle Changes

• Avoid scratching or squeezing the bumps to prevent autoinoculation.
• Do not share towels, clothing, or bath sponges.
• Cover lesions with watertight bandages during swimming or contact sports.

Patient Counseling & Advice

Inform the patient/parents that the condition is benign and self-limiting, though it may take 1 to 2 years for all lesions to fully disappear. Explain the 'BOTE sign', where bumps get red and angry before they go away, and reassure them this is a normal immune response, not an infection.

Follow-Up & Monitoring Schedule

Re-evaluation in 4-6 weeks if undergoing active treatment (like cryotherapy) to treat newly emerged lesions due to the long incubation period.

Preventive Strategies

Strict personal hygiene. Condom use provides incomplete protection for genital molluscum as lesions may occur on uncovered areas like the lower abdomen and thighs.

Excellent for immunocompetent individuals with complete, scarless resolution typical. Severe and prolonged courses are seen in immunocompromised patients (e.g., HIV), requiring HAART to restore immune function for clearance.