Molluscum

OVERVIEW: What every practitioner needs to know

Are you sure your patient has molluscum contagiosum? What should you expect to find?

Patients with molluscum present with firm, umbilicated shiny papules on the skin.

Papules:

These present as shiny, often grouped, firm umbilicated papules that most commonly range in size from 1mm to 1cm in diameter (Figure 1).
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Associated findings:

Individual lesions may have surrounding erythema and/or scale.

Patients may have associated itch in the area of the lesions.

Lesions can be spread by trauma or shaving and may be arranged in a linear fashion.
Location:

Lesions in adults are most often sexually transmitted and are located on the genitals, suprapubic area, and/or inner thighs.

Lesions may also occur in the skin folds, including axillae, antecubital and popliteal fossae, and the crural folds.

Widespread lesions, particularly with involvement of the face, or giant lesions (>1cm), may occur in immunocompromised patients.
Natural history:

Individual papules may last 2 months or longer.

Immunocompetent patients may clear the lesions without treatment, and immunocompromised patients may have lesions that persist for years (or indefinitely) and are refractory of treatment.

Molluscum commonly presents as shiny, often grouped, firm umbilicated papules.

How did the patient develop molluscum? What was the primary source from which the infection spread?

Molluscum is acquired from skin-to-skin spread, including sexual transmission, casual contact, autoinoculation (the Koebner phenomenon), and, less commonly, fomites.

Which individuals are of greater risk of developing molluscum?

Molluscum most commonly affects sexually active adults, patients with impaired cellular immunity, and children.
It occurs most commonly in individuals aged between 15 and 29 years.

Beware: there are other diseases that can mimic molluscum:

Other diseases that can mimic individual localized lesions, especially in the genital areas, include verruca, benign adnexal tumors (such as syringomas), pyoderma, or condyloma acuminatum.
In immunocompromised hosts, molluscum may mimic disseminated deep fungal infections, such as cryptococcosis, penicilliosis, and histoplasmosis (Figure 2, Figure 3). Cryptococcosis particularly can manifest with umbilicated and crusted papules on the skin, which may be difficult to distinguish from diffuse molluscum without a skin biopsy (Figure 4). Histologic analysis should allow for the definitive distinction of molluscum from deep fungal infection. Patients with cutaneous deep fungal infections from disseminated disease, such as cryptococcosis, often have associated systemic signs, such as fever, headache, and meningismus, which may help in making the diagnosis.
Giant lesions of molluscum may mimic a cutaneous malignancy, such as a basal cell carcinoma or keratoacanthoma, or an epidermal cyst.

Diffuse large molluscum on the forehead of an AIDS patient – this may be clinically confused with a disseminated deep fungal infection.

Disseminated cutaneous histoplasmosis on the forehead, manifesting as verrucous papules and plaques.

Disseminated cryptococcosis on the forehead, manifesting as variably sized nodules. Patient had cryptococcal meningitis as well.

What laboratory studies should you order and what should you expect to find?

Results consistent with the diagnosis

Laboratory studies are not typically helpful in making this diagnosis.

Results that confirm the diagnosis

If the diagnosis needs to be confirmed with testing, a skin biopsy may be helpful. The skin biopsy of molluscum will show:

large intracytoplasmic inclusion bodies in affected epidermal keratinocytes
an epidermal invagination possibly surrounding the inclusion bodies
surrounding dermal inflammation is also possible

What imaging studies will be helpful in making or excluding the diagnosis of molluscum?

Imaging studies are not helpful in making this diagnosis.

What consult service or services would be helpful for making the diagnosis and assisting with treatment?

Dermatology can be helpful in making with diagnosis and assisting with treatment.

If you decide the patient has molluscum, what therapies should you initiate immediately?

Lesions of molluscum may resolve spontaneously, and immediate treatment may not be required. In patients with extensive disease, or in immunnocompromised patients who may be at risk for extensive or persistent disease, there are several treatment options (Table I). These treatment options include topical therapies, such as topical acids, podophyllotoxin, cantharidin, imiquimod, tretinoin, adapalene, and topical cidofovir. Physical destructive methods are also helpful, and these include curettage, pulsed dye laser, cryotherapy, and photodynamic therapy. Systemic therapy, including intralesional Candida antigen, cimetidine, and subcutaneous interferon alpha, have been used but have not proven to be as effective as topical therapies.

Table I.

Type of Treatment	Medication	Instructions for use	Evidence level
Topical	Topical salicylic acid gel 12%	Apply to lesions twice weekly	A
Topical	Podophyllotoxin 0.5% solution	Apply to lesions daily	B
Topical	Imiquimod	Apply three times weekly for 12 weeks	A
Topical	Tretinoin 0.05% or 0.1%	Apply twice daily	E
Topical	Cantharidin	Apply once to lesions for 4–6 hours	B
Topical	Cidofovir 3%	Apply daily for five days per week for 8 weeks	E
Destructive	Cryotherapy	In-office application of liquid nitrogen	C
Destructive	Curettage	In-office procedure	C
Destructive	Pulsed-dye laser	In-office procedure	C
Systemic	Intralesional Candida antigen	In-office intralesional injection	C

Complications of topical therapies, including acids, podophyllotoxin, cantharidin, and imiquimod include local skin irritation, erythema, pain, and ulceration. Topical tretinoin and adapalene may also cause local skin irritation and erythema. Cryotherapy may lead to crusting of lesions, blister formation, ulcerations, and local pain. Curettage is a local surgical treatment, and there may be postprocedure pain and wound care needed.

What complications could arise as a consequence of molluscum?

Molluscum itself does not typically lead to complications, but lesions may become widespread and psychologically devastating, especially in immunocompromised patients. Lesions are highly infectious and may be passed from person to person.

What should you tell the family about the patient's prognosis?

The prognosis for molluscum infection is good, since it is an infection that only involves the skin.

How do you contract molluscum and how frequent is this disease?

Molluscum most commonly affects sexually active adults, patients with impaired cellular immunity, and children. It occurs most commonly in individuals aged between 15 and 29 years but can affect anyone. Molluscum is acquired from skin-to-skin spread, including sexual transmission, casual contact, autoinoculation (the Koebner phenomenon), and, less commonly, fomites.

Molluscum occurs worldwide and primarily affects young people and sexually active individuals. There is no seasonal variation.

There are no reports of zoonotic transmission.

What pathogens are responsible for this disease?

Molluscum is caused by molluscum contagiosum, which is a virus of the Molluscipox genus. Molluscum is the most common poxvirus infection in humans.

How do these pathogens cause molluscum?

Molluscum is acquired from skin-to-skin spread, including sexual transmission, casual contact, autoinoculation (the Koebner phenomenon), and, less commonly, fomites. The virus contacts skin and infects epidermal keratinocytes.

What other clinical manifestations may help me to diagnose and manage molluscum?

It is important to ask about contacts with similar lesions and sexual history. If lesions are only present locally, they are easier to manage, as topical and local destructive methods are often more effective in these cases. Widespread disease is very difficult to treat, because this often occurs in immunocompromised patients with refractory disease and the treatments are not well utilized in widespread disease. Lesions often have a central umbilication, which may be easier to visualize with a magnifying lens or once the lesions are frozen with cryotherapy. The umbilication is not always clinically obvious. The lesions are dome shaped, smooth, and often shiny. Occasionally, the central core of infected keratinocytes can be extracted with pressure and appear as a white, cheesy material.

What other additional laboratory findings may be ordered?

Skin biopsies are the most reliable confirmatory testing that can be performed.

How can molluscum be prevented?

Molluscum can be prevented by avoiding skin-to-skin contact with infected individuals.

WHAT'S THE EVIDENCE for specific management and treatment recommendations?

Diven, DG.. “An overview of poxviruses”. J Am Acad Dermatol. vol. 44. 2001. pp. 1-16. (This overview of poxviruses highlights molluscum, including clinical characteristics, differential diagnosis, diagnosis, and treatment.)

Mancini, AJ, Shani-Adir, A., Bolognia, JL, Jorizzo, JL, Rapini, RP. “Other viral diseases”. Dermatology. 2008. pp. 1229-32. (This is an outstanding overview of Molluscum contagiosum, including its relationship to immunocompromised patients.)

Gordon, PM, Benton, EC., Lebwohl, MG, Heymann, WR, Berth-Jones, J, Coulson, I. “Molluscum contagiosum”. Treatment of skin disease comprehensive therapeutic strategies. 2010. pp. 442-5. (This book evaluates the evidence for treatments for many different diseases of the skin. It grades them as A: double-blind studies, B: clinical trial with greater than or equal 20 subjects, C: clinical trial with less than 20 subjects, D: case series of more than 4 subjects, and E: anecdotal case reports.)

Martin, P.. “Interventions for molluscum contagiosum in people infected with human immunodeficiency virus: a systematic review”. Int J Dermatol.. 2016 Mar 18. (This review concludes that studies of treatment of molluscum in HIV-infected patients are of poor quality and do not permit evidence-based recommendations.)

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