Molluscum

DOJ Contents

Molluscum Contagiosum Daniel Hanson and Dayna G. Diven Dermatology Online Journal 9(2): 2 Primary Health, Boise, Idaho USA

Abstract

Molluscum contagiosum is a disease caused by a poxvirus of

the Molluscipox virus genus that produces a benign self-limited

papular eruption of multiple umbilicated cutaneous tumors. This

common viral disease is confined to the skin and mucous

membranes. Transmission requires direct contact with infected

hosts or contaminated fomites. It is generally thought to infect

humans exclusively, but there are a few isolated reports of

Molluscum contagiosum occurring in chickens, sparrows, pigeons,

chimpanzees, kangaroos, a dog, and a horse. The infection is found

worldwide and has a higher incidence in children, sexually active

adults, and those who are immunodeficent.

Introduction

Molluscum contagiosum, a cutaneous and mucosal eruption

caused by a Molluscipox virus, was first described and later

assigned its name by Bateman in the beginning of the nineteenth

century.[1] In 1841 Henderson and Paterson described the

intracytoplasmic inclusion bodies now known as molluscum or

Henderson-Paterson bodies.[2] In the early twentieth century,

Juliusberg, Wile, and Kingery were able to extract filterable virus

from lesions and show transmissibility.[3,4] Goodpasture later

described the similarities of molluscum and vaccinia.[5] Though

generally thought to infect only humans, case reports of the virus

occurring in other animals have been published. [6,7,8,9]

Incidence

Molluscum contagiosum virus (MCV) can be found

worldwide with a higher distribution in the tropical areas. The

disease is more prevalent in children with the lesions involving the

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face, trunk, and extremities. In adults the lesions are most

often found near the genital region. The disease is endemic with a

higher incidence within institutions and communities where

overcrowding, poor hygiene, and poverty potentiate its spread.[10]

Over the last 30 years its incidence has been increasing, mainly as

a sexually transmitted disease, and it is particularly rampant as a

result of concurrent human immunodeficiency virus (HIV)

infection.[11] The worldwide incidence is estimated to be between

2% and 8%.[12] Less then 5% of the children in the United States

are believed to be infected. Between 5% and 20% of patients with

HIV have symptomatic MCV.[13,14] There are four main subtypes

of molluscum contagiosum: MCV I, MCV II, MCV III, and MCV

IV.[15,16] All subtypes cause similar clinical lesions in genital and

nongenital regions. Studies show MCV I to be more prevalent

(75%–90%) than MCV II, MCV III, and MCV IV, except in

immunocompromised individuals.[17,18] There are, however,

regional variations in the predominance of a given subtype and

differences between individual subtypes in different countries.[19]

Pathogenesis

This disease is transmitted primarily through direct skin

contact with an infected individual. Fomites have been suggested

as another source of infection, with molluscum contagiosum

reportedly acquired from bath towels, tattoo instruments, and in

beauty parlors and Turkish baths.[10] The average incubation time

is between 2 and 7 weeks with a range extending out to 6 months.

Infection with the virus causes hyperplasia and hypertrophy of the

epidermis.[12] Free virus cores have been found in all layers of the

epidermis. So-called viral factories are located in the malpighian

and granular cell layers.[12] The molluscum bodies contain large

numbers of maturing virions. These are contained intracellularly in

a collagen-lipid-rich saclike structure that is thought to deter

immunological recognition by the host.[20] Rupture and discharge

of the infectious virus-packed cells occur in the center of the lesion.

MCV induces a benign tumor instead of the usual necrotic pox

lesion associated with other poxviruses.[21]

Clinical manifestations

MCV produces a papular eruption of multiple umbilicated

lesions. The individual lesions are discrete, smooth, and dome

shaped. They are generally skin colored with an opalescent

character. The central depression or umbilication contains a white,

waxy curdlike core. The size of the papule is variable, depending

upon the stage of development, usually averaging 2–6 mm. Papules



may exceed 1 cm in size in immunosuppressed hosts. The

papules may become inflamed spontaneously or after trauma and

present atypically in size, shape, and color. The lesions are often

grouped in small areas but may also become widely disseminated.

Any cutaneous surface may be involved, but favored sites

include the axillae, the antecubital and popliteal fossae, and the

crural folds. Rarely, MCV lesions occur in the mouth or

conjunctivae.[22,23,24] Autoinoculation is common. Children

usually acquire molluscum nonsexually at both genital and

nongenital areas. MCV in adults affects the groin, genital area,

thighs, and lower abdomen and is often acquired sexually. Around

10% of cases develop an eczematous dermatitis around the lesions,

but this disappears as the infection resolves.[25] Patients with

atopic dermatitis can have a disseminated eruption. Eruptions in

immunocompromised indiviuals are very resistant to treatment.

[13,26]

Dermatopathology

Histologically, molluscum contagiosum exhibits

intraepidermal lobules with central cellular and viral debris. In the

basal layer, enlarged basophilic nuclei and mitotic figures are seen.

Progressing upward, the cells show cytoplasmic vacuolization and

then eosinophilic globules. The nucleus becomes compressed at the

level of the granular cell layer, and the molluscum bodies lose their

internal structural markings. Undisrupted lesions show an absence

of inflammation, but dermal changes can include an infiltrate that

is lymphohistiocytic, neutrophilic, or granulomatous. The latter has

been seen in solitary lesions. Antibody to MCV by indirect

immunofluorescence has been found in 69% of patients with

visible lesions.[27] Polymerase chain reaction can detect MCV in

skin lesions.[28] Currently, there is no in-vitro or animal model for

MCV. MCV can undergo an abortive infection in some cell lines,

which can cause confusion with herpes simplex virus by

laboratories.[29] Two sets of investigators have infected human

skin with molluscum contagiosum and grafted it onto athymic

mice, although there was no continued viral replication.[30,31]

Diagnosis

The clinical appearance of molluscum contagiosum is in most

cases diagnostic. Though molluscum cannot be cultured in the

laboratory, histological examination of a curetted or biopsied lesion

can also aid in the diagnosis in cases that are not clinically obvious.

The thick white central core can be expressed and smeared on a



slide and left unstained or stained with Geimsa, Gram, Wright,

or Papanicolaou stains to demononstrate the large brick-shaped

inclusion bodies. Electron microscopy has also been used to

demonstrate the poxivirus structures. Immunohistochemical

methods using a polyclonal antibody allows recognition of

molluscum contagiosum in fixed tissue.[32] In-situ hybridization

for MCV DNA has also been utilized.[33] Molluscum contagiosum

lesions must be differentiated from verruca vulgaris, condyloma

accuminata, varicella, herpes simplex, papillomas, epitheliomas,

pyoderma, cutaneuos cyptococcosis, epidermal inclusion cyst,

basal cell carcinoma, papular granuloma annulare,

keratoacanthoma, lichen planus, and syringoma or other adenexal

tumors.

Treatment

Molluscum cantagiosum is a self-limited disease, which, left

untreated, will eventually resolve in immunocompetent hosts but

may be protracted in atopic and immunocompromised individuals.

Some patients pick and scratch at the lesions, a habit that may lead

to scarring. In addition, some schools and daycare centers will not

admit children with visible molluscum papules. When patients seek

medical attention and desire to rid themselves of the papules, there

are several means of therapeutic destruction to help speed

resolution. The decision whether treatment is necessary depends on

the needs of the patient, the recalcitrance of their disease, and the

likelihood of treatments to leave pigmentary alteration or scarring.

Most of the common treatments consist of various means to

traumatize the lesions. Antiviral and immune-modulating

treatments have recently been added to the options. The following

is a brief summary of some of the more common treatments.

Cryosurgery

One of the most common, quick, efficient methods of

treatment is cryotherapy. Liquid nitrogen, dry ice, or Frigiderm are

applied to each individual lesion for a few seconds. Repeat

treatments in 2–3-week intervals may be required.[34] Hyper- or

hypopigmentation and scarring may be caused by this treatment.

Evisceration

An easy method to remove the lesions is eviscerating the core

with an instrument such as a scalpel, sharp tooth pick, edge of a

glass slide, or any other instrument capable of removing the



umbilicated core. Because of its simplicity, patients, parents,

and caregivers may be taught this method so new lesions can be

treated at home.[35,36] This method is simple but may not be

tolerated by small children.

Curettage

Curettage is another method of removal. It can be used with

and without light electrodessication. This method is more painful,

and it is recommended that a topical anesthetic cream be applied to

the lesions before the procedure to decrease the pain. This method

has the advantage of providing a reliable tissue sample to confirm

the diagnosis.[35,37]

Tape stripping

Another reported treatment involves the use of adhesive tape.

The adhesive side of the tape is repeatedly applied to and removed

from the lesion for 10–20 cycles. This action effectively removes

the superficial epidermis from the top of the lesion.[38] However,

repeated use of the same strip has the potential to spread the virus

to adjacent, uninvolved skin.

Podophyllin and podofilox

A 25% suspension in a tincture of benzoin or alcohol may be

applied once a week. This treatment requires some precautions. It

contains two mutagens, quercetin and kaempherol. Some of the

listed side effects include severe erosive damage in adjacent

normal skin that may cause scarring and systemic effects such as

peripheral neuropathy, renal damage, adynamic illeus, leucopenia,

and thrombocytopenia, especially if used generously on mucosal

surfaces. Podofilox is a safer alternative to podophyllin and may be

used by the patient at home. The recommended use usually consists

of application of 0.05 ml of 5% podofilox in lactate buffered

ethanol twice a day for 3 days.[35,38] The active agent is

absolutely contraindicated in pregnancy.

Cantharidin

Cantharidin (0.9% solution of collodian and acetone) has been

used with success in the treatment of MCV. This blister-inducing

agent is applied carefully and sparingly to the dome of the lesion

with or without occlusion and left in place for at least 4 hours



before being washed off. Cantharidin can cause severe

blistering. It should be tested on individual lesions before treating

large numbers of lesions. It should not be used on the face. When

tolerated, this treatment is repeated every week until the lesions

clear. Usually 1–3 treatments are necessary.[39]

Iodine solution and salicylic acid plaster

A 10% iodine solution is placed on the molluscum papules

and, when dry, the site is covered with small pieces of 50%

salicylic acid plaster and tape. The process is repeated daily after

bathing. After the lesions have become erythematous in 3–7 days,

only the iodine solution is applied. Resolution has been reported in

a mean of 26 days.[40] Maceration and erosion can result.

Tretinoin

Tretinion 0.1% cream has been used in the treatment of MCV.

It is applied twice daily to the lesions. Resolution was reported by

day 11. Trace erythema at the site of prior lesions was a noted side

effect.[41] Tretinion 0.05% cream has also been used with success

and decreased irritation.[35]

Cimetdine

Oral cimetidine has successfully been used in extensive

infections.[42] The histamine 2-receptor antagonist stimulates

delayed-type hypersensivity. One uncontrolled study showed

resolution in 9 of 13 patients. In this study, the dosage was 40

mg/kg/day in two divided doses for 2 months.[43] The authors

recommended further placebo-controlled, double-blind studies be

completed to determine the efficacy of cimetidine in treating MCV.

Because cimetadine interacts with many systemic medications, a

review of the patient's other medications is recommended.

Potassium hydroxide

Another treatment option is the use of potassium hydroxide. In

one study, an aqueous solution of 10% KOH was applied topically

twice daily to all lesions with a swab. The treatment was

discontinued when an inflammatory response or superficial ulcer

became evident. Resolution occurred in a mean of 30 days.[44]

This treatment had some complications including hypertrophic scar

formation and persistent or transitory hyper- and



hypopigmentation. A subsequent study in pediatric patients

recommended the use of 5% KOH and found it equally effective

with many fewer side effects.[45]

Pulsed dye laser

The use of pulsed dye laser for the treatment of MC has also

been documented with excellent results. The therapy was well

tolerated, without scars or pigment anomalies. The lesions resolved

without scarring at 2 weeks. Studies show 96%–99% of the lesions

resolved with one treatment.[46,47] The pulsed dye laser is quick

and efficient, but its expense makes it less cost effective than other

options.

Imiquimod

Imiquimod 5% cream has been used topically to treat MCV by

inducing high levels of IFN-α and other cytokines locally.[48,49]

This potent immunomodulatory agent is well tolerated, although

application site irritation is common. It has had no known systemic

or toxic effects in children.[50] It is applied to the area nightly for 4

weeks. Clearing can take up to 3 months.

Cidofovir

Cidofovir is a nucleoside analog that has potent antiviral

properties. Several small studies and case reports describe the

successful use of cidofovir applied topically or administered by

intralesional injection in several virally induced cutaneous diseases.

[51] Cidofovir cream 3% has been used successfully to treat MCV

in studies, with clearing in 2–6 weeks.[52] Its high cost, need for

extemporaneous preparation, and carcinogenicity in some studies

have limited its use.[51]

Conclusion

Molluscum Contagiosum is a common, generally benign, viral

infection of the skin. It is common in children, sexually active

adults, and immunodeficient patients. It is caused by the

molluscipox virus, a member of the poxviridae family. This virus

differs from other poxviruses in that it causes spontaneously

regressing, umbilicated tumors of the skin rather than poxlike

vesicular lesions. In immunocompetent, nonatopic patients

molluscum contagiosum is usually a self-limited disease for which



treatment is not mandatory. However, when treatment is

deemed appropriate, multiple local therapeutic options are

available. For patients with impaired immune functions with

widespread and potentially disfiguring eruptions, the usual local

destructive therapies are ineffective; antiviral and

immunomodulatory medications have been more successful.

References

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