Molluscum contagiosum

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Introduction

Molluscum contagiosum is a contagious dermatological infection that predominantly affects children. It is caused by a poxvirus and presents as clusters of small umbilicated papules.

Molluscum infection is common. Exact estimates of overall prevalence vary, from 2-15% depending on the population studied (particularly age, country and comorbidities).2-3

It is most common in young children under the age of 10, decreasing in prevalence with increasing age. Molluscum is most common in warm, tropical environments.


Aetiology

Molluscum is caused by cutaneous infection with molluscum contagiosum virus, a dsDNA poxvirus.1

It is transmitted through direct skin-to-skin contact, or indirectly via fomites. Transmission may also occur through autoinoculation, as children scratch localised clusters of lesions and spread them further. Genital lesions may be spread through sexual contact.


Risk factors

Key risk factors for contracting and transmitting molluscum infection include:

  • Direct contact: skin-to-skin contact with lesions.
  • Water-borne spread: spread through shared bathwater or pool water, usually warm water.
  • Fomites: sharing clothes or towels that may serve as fomites.
  • Environment: transmission is more common in warm, tropical, humid environments.
  • Immunocompromise: HIV infection or immunosuppressive medication increases the risk of infection with molluscum and may also lead to lesions that are more persistent and recurrent, even in adults.3

Clinical features

History

Patients (or more likely, their parents) will report the appearance of lesions, usually within 2 weeks (but sometimes up to 6 months) of exposure. Siblings or close contacts may also be affected. Although mostly asymptomatic some may be itchy but are not painful.4

Clinical examination

Molluscum lesions appear as small, round, pearly epidermal papules (raised bumps) with central umbilication. They are generally 2-6mm in diameter but can be larger (giant mollusca). Lesions may become inflamed or crusted as they heal and resolve. Molluscum may induce secondary local dermatitis, leading to surrounding erythema.4

They tend to appear in localised crops, particularly on the trunk, or in warm, moist places such as the axillae, groin, and popliteal fossae. They may appear in rows if they are autoinoculated due to scratching, known as pseudo-koebnerisation.

Representative images in diverse skin types

Because of image reproduction rules, we are only able to directly include images with creative commons licencing. Unfortunately, the majority of images of dermatological conditions available under this licence are in Caucasian patients and fair skin tones.

We have included representative images here that we are not able to reproduce in this article directly, which we encourage you to review.

Associated conditions

Molluscum dermatitis

A significant minority of children with molluscum infection develop dermatitis surrounding the lesions. This usually occurs in children who have pre-existing atopic dermatitis that is exacerbated by molluscum infection, rather than molluscum causing dermatitis in children without a history of atopy.

Molluscum infections may be more common in children with dermatitis, due to disruptions in the integrity of the skin barrier.7 This dermatitis can be treated with emollients, and corticosteroids if needed.

Human immunodeficiency virus (HIV)

Human immunodeficiency virus (HIV) increases the likelihood and severity of many cutaneous infections, including molluscum. In patients with HIV, molluscum infection is typically more widespread, with larger and atypical lesions. Lesions may be more persistent and may recur.3


Differential diagnoses 

Differential diagnosis Similarities Differences Image

Viral warts

Small, epidermal lesions that may appear in crops

Have a hard, keratinous, irregular surface

Will affect the palms and soles of feet

Viral warts
Figure 3. Viral warts.8

Investigations

Molluscum is diagnosed clinically, and in most cases does not require any further investigations. If a patient has a persistent or unusual infection, particularly with lesions persisting beyond 2 years in duration or those that are unusually numerous, large or atypical in shape, further investigation for underlying conditions should be considered, particularly if in a region with a high prevalence of HIV.


Management

General advice

As molluscum is self-limiting, specific treatment is not necessarily required, particularly if the lesions can be readily covered with clothing or plasters to prevent spread to others and auto-inoculation.

Good hygiene measures, such as avoiding scratching, regular handwashing and washing of clothes, are important. Although molluscum is a contagious infection, it does not require children to be kept home from school.

Therapies

There are no specific treatments for molluscum. It is important to discuss with the patient that the natural history of the infection does not necessitate treatment, as it will resolve on its own.

If patients would like treatment, options for physical treatment include removing the soft, white, umbilicated core of the lesions (by gently pricking and squeezing the lesions, being careful to avoid auto-inoculation). Other options include cryotherapy, curettage, or laser ablation, although these can leave white marks or scars, and will require local anaesthetic in children.

Medical treatment options include wart paints containing salicylic acid and cantharidine solution. Topical imiquimod therapy is sometimes used, but there is mixed evidence for this.9-10


Complications

Molluscum infection is self-limiting and will resolve even without treatment (typically within 6 months).

Recurrences are uncommon in immunocompetent patients, although re-infection can occur.

Secondary bacterial infection (impetigo) can occur, particularly if children scratch their lesions. For some patients, molluscum lesions may leave small, pitted scars.


Key points

  • Molluscum is a common, contagious viral dermatological infection that is common among young children.
  • Molluscum appears as crops of small, umbilicated, pearly papules, commonly in the axillae and groin. These are generally asymptomatic but may be itchy.
  • Treatment is not usually required as the infection is usually self-limiting, and there are no specific therapies available.

Reviewer

Consultant Dermatologist


Editor

Dr Chris Jefferies


References

  1. UptoDate. Molluscum contagiosum. 2020. Available from: [LINK]
  2. Koning et al. Molluscum contagiosum in Dutch general practice. 1994. Available from: [LINK]
  3. WHO. Guidelines on the Treatment of Skin and Oral HIV-Associated Conditions in Children and Adults. 2014. Available from: [LINK]
  4. Australasian College of Dermatologists. Molluscum contagiosum. 2015. Available from: [LINK]
  5. Wikimedia Commons. Molluscum contagiosum on the thigh of a Caucasian child. Licence: [CC BY-SA]. Available from: [LINK]
  6. DermNet NZ. Molluscum crop in a linear pattern, possibly due to autoinoculation due to scratching. Licence: [CC BY-NC-ND]. Available from: [LINK]
  7. DermNet NZ. Complications of atopic dermatitis. 2004. Available from: [LINK]
  8. Wikimedia Commons. Plantar warts on the sole of a toe. Licence: [CC BY-SA]. Available from: [LINK]
  9. van der Wouden et al. Interventions for Cutaneous Molluscum Contagiosum. 2017. Available from: [LINK]
  10. eTG Complete. Molluscum contagiosum. 2020. Available from: [LINK]

 

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