Molluscum Contagiosum

Definition, Etiology, Pathogenesis Top

Molluscum contagiosum is a chronic inflammatory viral skin disease that causes characteristic papular epidermal lesions.

1. Etiologic agent: Molluscum contagiosum virus (MCV), which replicates exclusively in squamous epithelial cells, does not spread into the deeper layers of skin, and does not cause viremia.

2. Reservoir and transmission: Humans are the only reservoir for MCV. Infection spreads through direct contact with the infected skin (including sexual contacts) or via contaminated clothing, towels, and other objects. Autoinoculation is frequent; this causes the lesions to spread to unaffected areas and leads to the persistent course of the disease.

3. Incubation and contagious period: The incubation period is 2 to 12 weeks (up to 6 months). The patient is contagious for the entire duration of cutaneous lesions.

Clinical Features and Natural History Top

The primary cutaneous lesions are firm, smooth, flesh-colored or lighter papules, measuring from 1 to 5 mm in diameter (in immunocompromised individuals >5 mm [so-called giant molluscum contagiosum]). Older lesions may be characteristically umbilicated with a dimple at the center, which is particularly visible when the lesion is illuminated from the side by a strong light source. The papule may be surrounded by a discolored or erythematous rim. In immunocompetent individuals, the number of lesions ranges from 1 to 30. In adolescents and adults, they are most frequently found on the inner thigh, external genital area, pubic area, and lower abdomen; in young children, on the face, eyelids, trunk, and extremities; in immunocompromised patients, the lesions are disseminated and numerous (up to several hundred). The lesions are otherwise asymptomatic, only rarely producing discomfort upon healing (in the case of intense inflammation or eczema).

In immunocompetent individuals, the infection resolves spontaneously over 6 to 18 months, occasionally persisting for up to 4 years. Receding lesions may be accompanied by a local inflammatory reaction (mild erythema, irritation), which indicates an active cell-mediated immune response (the clinical manifestation of recovery). Healed lesions may leave the dimples, which subsequently disappear or evolve into point-like scars.

Autoinoculation, secondary bacterial infection (in particular if the lesions are being scratched), and scarring may complicate the course of the disease.

Diagnosis Top

Diagnosis is based on the clinical presentation. In equivocal cases microscopic examination of smears of the contents of the lesions or skin biopsy material stained with Wright or Giemsa stain may reveal cytoplasmic inclusions (“molluscum bodies”).

Differential Diagnosis

1. Spitz nevus, epitheliomas (eg, basal cell carcinoma), juvenile xanthogranuloma, common warts, condylomata acuminata, milia, keratosis pilaris, lichen nitidus, and sebaceous or sudoriferous cysts.

2. Disseminated lesions in patients with impaired cell-mediated immune response should be differentiated from disseminated cryptococcosis or histoplasmosis.

3. In patients with inflammatory molluscum contagiosum, exclude bacterial skin infections (eg, folliculitis, furuncle).

Treatment Top

Most lesions in low-risk patients are self-limiting and do not require treatment. If judged needed (eg, for esthetic reasons, or in the case of multiple, persistent, or refractory lesions, repeated development of new lesions, or autoinoculation) a number of treatments may be tried. However, most evidence is of low quality and cannot be recommended with confidence.Evidence 1Weak recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to numerous studies lacking blinding, imprecision, and high rate of drop-out; confidence is somehow higher for podophyllotoxin and laser treatments. van der Wouden JC, van der Sande R, Kruithof EJ, Sollie A, van Suijlekom-Smit LW, Koning S. Interventions for cutaneous molluscum contagiosum. Cochrane Database Syst Rev. 2017 May 17;5:CD004767. doi: 10.1002/14651858.CD004767.pub4. Review. PubMed PMID: 28513067; PubMed Central PMCID: PMC6481355. Syed TA, Lundin S, Ahmad M. Topical 0.3% and 0.5% podophyllotoxin cream for self-treatment of molluscum contagiosum in males. A placebo-controlled, double-blind study. Dermatology. 1994;189(1):65-8. PubMed PMID: 8003791. Binder B, Weger W, Komericki P, Kopera D. Treatment of molluscum contagiosum with a pulsed dye laser: Pilot study with 19 children. J Dtsch Dermatol Ges. 2008 Feb;6(2):121-5. Epub 2007 Nov 9. English, German. PubMed PMID: 17995966. Omi T, Kawana S. Recalcitrant molluscum contagiosum successfully treated with the pulsed dye laser. Laser Ther. 2013;22(1):51-4. PubMed PMID: 24155550; PubMed Central PMCID: PMC3799048. Handjani F, Behazin E, Sadati MS. Comparison of 10% potassium hydroxide solution versus cryotherapy in the treatment of molluscum contagiosum: an open randomized clinical trial. J Dermatolog Treat. 2014 Jun;25(3):249-50. doi: 10.3109/09546634.2013.832135. Epub 2013 Aug 27. PubMed PMID: 23924070. According to authors of one Cochrane review, “no randomised trials for several commonly used treatments, such as expressing lesions with an orange stick or topical hydrogen peroxide” could be found. And “since most lesions resolve within months, unless better evidence for the superiority of active treatments emerges, molluscum contagiosum can be left to heal naturally.”

Antiviral Treatment

1. Pharmacologic treatment (please note above the comment regarding questionable, if any, efficacy):

1) Topical imiquimod (cream) 3 times per week for 4 to 16 weeks: Apply to the affected areas overnight (6-10 hours), wash off in the morning.

2) Topical podophyllotoxin cream or solution may also be considered, particularly in men; use with caution in women of childbearing age.

3) Highly active antiretroviral therapy (HAART) is associated with the resolution of lesions in HIV-positive patients (data is limited).

2. Invasive treatment (according to authors of the Cochrane review, the evidence for effectiveness of physical destruction of molluscum is very limited and, until this changes, awaiting spontaneous resolution of molluscum lesions remains a strong option):

1) Laser therapy: Effective, associated with a low risk of scarring or discoloration.

2) Liquid nitrogen spray cryotherapy in the case of a limited number of lesions; possible complications include blisters and scars. In some patients the procedure may need to be repeated every 2 to 4 weeks.

3) Curettage or needle extraction under local anesthesia may be used in patients with a limited number of lesions.

Follow-Up Top

In the case of reasonable suspicion, examine adolescents and adults for the presence of other sexually transmitted diseases. If a treated lesion becomes tender or reveals erythema, edema, crusting, or purulent exudate (suggesting a secondary bacterial infection), administer topical antimicrobial treatment (less frequently, oral antimicrobial treatment is necessary). Disseminated lesions (in particular giant molluscum contagiosum) and lesions appearing on the face, neck, and scalp in adult patients are an indication for HIV testing.

Prognosis Top

In immunocompetent individuals the lesions resolve spontaneously. In severely immunocompromised patients the disease is protracted and produces giant, generalized, confluent, and disfiguring lesions, which are difficult to treat unless a normal immune function is restored.

Prevention Top

Sharing of clothing and towels as well as maintaining sexual contacts with infected individuals should be avoided. Examination of household contacts is recommended (the infection is frequently transmitted among household contacts). Lesions should not be rubbed or scratched (risk of autoinoculation).