Molluscum contagiosum (MC) is a self-limited infection caused by the double-stranded DNA molluscum contagiosum virus (MCV) in the Poxviridae family (Molluscipox genus)
Pathology demonstrates lobulated crateriform lesions often with an acanthotic epidermis. Infected cells show characteristic intracytoplasmic viral inclusions known as Henderson-Patterson bodies that often displace the cell's nucleus to the periphery. (Trcko et al; Open Forum Infect Disease, 2018)
Classic MC lesions are firm round shiny skin-colored or pink-papules with central umbilication.
MC is commonly encountered in the pediatric population but can also be observed in immunocompromised and in sexually active adults. It is typically transmitted by skin-to-skin contact but can also be inoculated onto the skin from infected surfaces (for example wrestling or gymnastics mats, towels, toys, razors, etc.). Molluscum dermatitis may develop in areas that are affected, with pruritus and scratching contributing to the further spread of these contagious lesions. Molluscum dermatitis is more common in atopics. Inflammation of individual lesions may lead to patient and/or parental concerns about infection, however, this inflammatory reaction is an indication of the development of a host immune response and often precedes the resolution of lesions.
When extensive in the genital area(s) in adults, the virus is sexually transmitted, and patients should be educated on the risk of transmission to their sexual partner(s).
Histopathology is rarely needed to make this diagnosis, although atypical clinical lesions may at times be biopsied demonstrating the classic features: (Trcko et al; Open Forum Infect Disease, 2018)
- Lobulated crateriform lesion
- Acanthotic epidermis
- Large intracytoplasmic inclusion bodies (Henderson-Patterson bodies) within epidermal keratinocytes
Multiple treatment modalities have been reported, although the efficacy of treatment is controversial. Treatments include but are not limited to: cryotherapy, electrodesiccation, curettage, manual extraction, imiquimod, cantharidin, cidofovir, podophyllotoxin, retinoids, TCA, KOH 10% sln, IL Candida Ag, cimetidine, etc. Disease is self-limited with the average duration around 6-12 months (range few months to several years). (Meza-Romero et al. Clin Cosmet Investig Dermatol 2019)
In a large meta-analysis from 2017, the effects of specific treatments and management strategies were evaluated in MC patients who were not immunosuppressed and had non-genital disease. The conclusion was that no single intervention was convincingly effective in the treatment of MC, and therefore the natural resolution of MC remains a strong method for dealing with the condition. (van der Wouden et al. Cochrane Database Syst Rev 2017) When lesions are cosmetically bothersome, in the genital area(s), extensive, or affecting the immunosuppressed, treatments can reduce the number of lesions. Just be aware that treatment may not alter the duration of disease.
Orthopoxviruses cause variola, vaccinia, cowpox and monkeypox. Pahology shows intracellular edema, ballooning degeneration and eventually reticular degeneration secondary to cell rupture. This results in multilocular vesicles. A characteristic finding in all four diseases is the presence of cytoplasmic eosinophilic inclusion bodies in infected keratinocytes known as Guarnieri bodies
Coxsackie virus is most commonly implicated in hand foot and mouth disease. Pathology of this lesion shows reticular degeneration with intraepidermal vesiculation.
Parapoxvirus causes Orf (aka ecthyma contagiuosum) and Milker nodules (aka paravaccinia). Both of these infections demonstrate similar histopathologic findings. Biopsy shows a symmetrical nodule with an overlying parakeratotic crust and significant epidermal acanthosis with strands of epidermis extending into the dermis. There is usually marked reticular degeneration and intraepidermal vesiculation.
Clinical Pearl: Molluscum contagiosum is caused by infections with poxvirus. Biopsy shows lobulated crateriform lesions often with an acanthotic epidermis. Infected cells show characteristic intracytoplasmic viral inclusions known as Henderson-Patterson bodies. Patients with genital molluscum should be educated on the risk of transmission to their sexual partner(s).
Other references:
(Badri et al. StatPearls 2019)
(Bolognia et al.)
