Molluscum Contagiosum

Molluscum contagiosum is a viral infection limited to the epidermis and is common in children below 5 years of age. Lesions appear as grouped, flesh-colored, dome-shaped papules with central umbilication. Molluscum contagiosum is mild in immunocompetent patients and self resolves within months. Immunocompromised individuals present with extensive lesions and systemic disease, which require treatment. Molluscum contagiosum is highly transmissible; therefore, patient education is key in its management. Cryotherapy with liquid nitrogen is the 1st-line treatment.

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Overview

Epidemiology

  • 1% of all diagnosed skin disorders
  • Usually presents in children < 5 years of age or adolescents
  • Increased incidence in hot, humid climates
  • Slight predominance in boys
  • More common in patients with:
    • HIV
    • Atopic dermatitis

Etiology and transmission

  • Molluscum contagiosum virus (MCV) is a double-stranded, linear, DNA poxvirus.
  • Transmission:
    • Exposure to infected individuals (skin-to-skin contact):
      • Sexually transmitted
      • Pre-partum
    • Fomites (e.g., towels, toys, razors)
    • Autoinoculation (scraping)

Pathophysiology

  • Incubation period from 2 weeks to 6 months
  • Virus infects only keratinocytes → localized to epidermis
  • Inhibits innate immunity via antiviral protein production → persistent infection

Histopathology

  • Hyperkeratosis (thickened epidermis)
  • Epidermal proliferation into the dermis
  • Henderson-Paterson bodies: inclusions visible in the keratinocytes of the basal, spinous, and granular layers of the epidermis
Henderson-Paterson bodies

Henderson-Paterson bodies:
Characteristic histological features of molluscum contagiosum. Henderson-Paterson bodies are inclusions that are visible in the keratinocytes of the basal, spinous, and granular layers of the epidermis.

Image: “Molluscum Contagiosum 1” by Ed Uthman. License: CC BY 2.0

Clinical Presentation and Diagnosis

Clinical presentation of lesions

  • Usually no systemic symptoms
  • Dermatological features:
    • Shape and color:
      • Dome shaped
      • Pearly papules
      • Flesh colored
      • 2–6 mm in diameter
      • Central umbilication
    • Usually multiple and occur in clusters
    • Rarely associated with pruritus or tenderness
    • Distribution:
      • Children: 
        • Face
        • Trunk
        • Axilla
        • Antecubital fossa
        • Popliteal fossa
      • Adults: 
        • Anogenital area
        • Abdomen
        • Thighs
      • Palms and soles not involved
  • Immunocompromised individuals may have widespread systemic illness.

Diagnosis

  • Clinical diagnosis is sufficient.
  • Histopathological analysis to confirm diagnosis
  • Lesions in inguinal region → STD panel to rule out accompanying STIs

Management

Treatment

  • No treatment is necessary for healthy individuals as it is a self-limiting disease.
  • Patient education:
    • Complete resolution can take up to 1 year.
    • Avoid sharing towels and sheets, and do not shave across lesions.
    • Cover lesions with a tight bandage.
    • Practice safe sex.
  • Management for cosmetic reasons or to reduce transmission:
    • Physical removal (1st-line therapy):
      • Cryotherapy (liquid nitrogen)
      • Curettage
      • Cantharidin (topical blistering agent to be applied only by a physician)
    • Topical treatment (applied by the patient):
      • Podophyllotoxin
      • Potassium hydroxide/salicylic acid
      • Benzoyl peroxide
      • Tretinoin
      • Topical imiquimod
      • Oral cimetidine
  • Immunocompromised patients:
    • Antiretroviral therapy for patients with HIV
    • Interferon-alpha or cidofovir

Prognosis

  • Spontaneous resolution within 1 year in immunocompetent individuals
  • ⅓ of patients may exhibit recurrence.

Complications

  • Cellulitis
  • Conjunctivitis (if present on the eyelids)
  • Abscess
  • Scarring/hypopigmentation after cryotherapy

Differential Diagnosis

  • Basal cell carcinoma: pearly skin lesions that may present as ulceration and mimic the lesions of molluscum contagiosum. Basal cell carcinoma is common in the elderly. Lesions are found in sun-exposed areas. A biopsy may be necessary to differentiate between basal cell carcinoma and molluscum contagiosum.
  • Condyloma acuminatum: flesh-colored pedunculate lesions secondary to HPV infection. Lesions are mainly present in the anogenital region. Condyloma acuminatum is usually sexually transmitted and can be prevented via vaccination. Treatment of lesions is similar to the approach used to treat molluscum contagiosum.
  • Condylomata lata: smooth flesh-like lesions appearing gray or white, located in the vaginal, penile, or anal area, occurring secondary to a syphilis infection. Condylomata lata is an STI and the treatment for primary syphilis is with antibiotics. Treatment of lesions in condylomata lata is similar to the approach used to treat the lesions in molluscum contagiosum. Patients should be examined for other STIs.
  • Herpes: a painful condition with ulcerating lesions caused by HSV that presents with systemic symptoms. Lesions are more pustular, blistering, and erythematous than those occurring in molluscum contagiosum. Treatment is supportive as infection cannot be completely eradicated. Outbreaks are treated with acyclovir.
  • Varicella zoster: an infection caused by the Varicella zoster virus. Flesh-colored lesions with central umbilication present with systemic manifestations of fever and coryza. The lesions are extremely pruritic. Varicella-zoster infections are self limiting and of short duration, and are typically treated only with supportive care in immunocompetent individuals. Infections can be prevented by vaccination.

References

  1. Badri, T., Gandhi, G.R. (2020). Molluscum Contagiosum. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK441898/
  2. Isaacs, S. (2021). Molluscum contagiosum. UpToDate. Retrieved February 15, 2021, from https://www.uptodate.com/contents/molluscum-contagiosum
  3. Coloe, J., Morrell, D.S. (2009). Cantharidin use among pediatric dermatologists in the treatment of molluscum contagiosum. Pediatr Dermatol. 26(4), 405–408. https://pubmed.ncbi.nlm.nih.gov/19689514/ 
  4. Braue, A., Ross, G., Varigos, G., Kelly, H. (2005). Epidemiology and impact of childhood molluscum contagiosum: A case series and critical review of the literature. Pediatr Dermatol. 22(4), 287–294. https://pubmed.ncbi.nlm.nih.gov/16060861/ 
  5. Brown, J., Janniger, C.K., Schwartz, R.A., Silverberg, N.B. (2006). Childhood molluscum contagiosum. Int J Dermatol. 45(2), 93–99. https://pubmed.ncbi.nlm.nih.gov/16445494/

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