Table of Contents
I. Introduction
• Definition of Molluscum Contagiosum
• Transmission of Molluscum Contagiosum
II. Clinical Presentation
• Appearance of Lesions
• Incubation Period
• Inflammatory Reactions in Children
III. Virology and Pathogenic Mechanisms
• MCV Proliferation and Antiviral Immunity
• Molluscum Bodies
IV. Evaluation and Differential Diagnosis
V. Management of MC
• Need for Therapy
• Treatment Options
• Use of Pulsed-Dye Laser Therapy
VI. Conclusion
Molloscum contagiosum (MC) is a benign condition limited to keratinocytes typically presenting pinkish purple color lesions appearing dome-shaped. MC is evident globally and is particularly common in children with lesions developing anywhere in the body. Among adults, it is observed as a sexually acquired condition affecting the genitals, pubic region, upper thighs and buttocks. The transmission occurs by two routes; either by the direct skin-to-skin contact or indirect contacts such as underclothes or towels. In utero and prepartum transmission of the infection has also been reported causing congenital molluscum contagiosum.
Clinical Presentation
The infection starts as a small single or multiple, white papules developing particularly on the genital region and the face. The lesions often present pearly appearance and are usually smooth and firm. They can range in size from that of a pin-head to 2-5 millimeters in diameter and in some cases may become sore, itchy and swollen. The incubation period is estimated to be somewhere between 2 weeks to 6 months. Atopic dermatitis is considered as a risk factor of developing MC because of the immune cell dysfunction in atopic skin. Immunocompromised patients such as HIV positive individuals can continue to develop giant lesions more than 15mm in diameters resistant to standard therapy. MC is recently classified as common skin lesions affecting children; the sexually transmitted lesions developing on the genitals, abdomen and inner thighs; and the diffuse and recalcitrant eruptions affecting immunosuppressed disorders.
Virology and Pathogenic Mechanisms
MC is a double-stranded DNA poxvirus and four major subtypes are identified based on DNA analysis; MCV-1 (98% affecting children), MCV-2 (causes skin lesions particularly among HIV individuals), MCV-3 and MCV-4 prevalent in Asia and Australia. Molloscum contagiosum virus (MCV) proliferates within the follicular epithelium separating layers 1 to 3 of CD34+ stromal cells. MCV produces proteins affecting the antiviral immunity, hence the development of innate immune response becomes affected. As MCV proliferates cytoplasmically, the internal organelles are dislocated as the infected cell continues to grow. The molluscum bodies are the viral particles that develop within the cytoplasmic vacuoles and are detected with special stains like phosphotungstic acid–hematoxylin preparation.
Inflammatory Reactions in Children
The inflammatory response is common among children causing pruritus and pain. There are several forms of inflammatory reactions developing in association with MC. The inflamed lesions associated with MC are characterized by swelling including pustular lesions. In a study conducted at a tertiary care pediatric dermatology practice, of all the 696 MC affected patients, molluscum dermatitis was identified in 38.8% of the cases, inflamed MC lesions accounted for 22.3% and Gianotti-Crosti syndrome-like reactions were evident among 4.9%. The Gianotti-Crosti syndrome-like reactions is characterized by an eruption of monomorphous, papulovesicles or erythematous papules separate from MC lesions and developed among 34 patients during the MC. Among 13 patients, the mean duration of GCLR was identified as 6 weeks and the treatment with topical corticosteroid greatly improved the condition within one week. As the inflammatory response among children is poorly studied, an improved understanding of the pathogenesis of the associated inflammatory reaction of MC can assist with the development of effective treatment.
Evaluation (screening) and differential diagnosis
The diagnosis is primarily based on the characteristic feature of the lesions and in the case of a diagnostic challenge, dermatoscopy may be beneficial by detecting a central white to a yellow amorphous area with branched vessels. If an atypical infection is identified, a biopsy may be performed to detect the histopathologic features. When diagnosis difficulty persists, polymerase chain reaction for molluscum can be used although it is not routinely performed.
In some cases, the MC may be incorrectly diagnosed as cysts, basal cell carcinoma, cutaneous horn and keratoacanthoma. The genital MC could also be mistaken as vulval lymphangioma circumscriptum and ectopic sebaceous glands. Among children, the differential diagnosis includes warts, syringoma and closed comedones.
Management of MC
As the infection can cure on its own, the treatment usually is not initiated especially in children. Among some of the individuals, the need for a therapy is required because of an underlying atopic disease. According to CDC, the treatment options of MC include physical removal including initiation of cryotherapy and laser therapy. Among children, the use of oral cimetidine is recommended as a safe management of MC. Podophyllotoxin cream (0.5%), iodine, potassium hydroxide, imiquimod and cantharidin are recommended as alternative options.
According to a recent publication titled ‘Treatments for Molluscum Contagiosum, a Common Viral Infection in Children’, a study assessed the effects of various treatments and management strategies for MC. It studied 22 trials conducted to evaluate and compare different treatment options for MC. It indicates that several common treatments for MC such as physical destruction are not sufficiently evaluated while other treatments were not part of the standard practice. The evidence found the infection not favoring any one single treatment and that natural resolution of MC continues to remain as an initial strategy for dealing with the condition.
Alternative Therapy with use of Pulsed-Dye Laser
In a systematic review conducted to determine the use of Pulsed-Dye laser (PDL) therapy for the treatment of MC, a search of National Library of Medicine’s database was performed that discussed the treatment of MC with PDL. In these articles, 161 patients were reviewed and over 4200 MC lesions were treated with PDL. The review concluded that PDL offers an effective treatment for MC and is considered safe, effective and well tolerated without causing permanent pigment change.
Outcomes
MC is a self-healing disease spontaneously clearing during its natural course with a mean duration for a single lesion as 2 months and the mean duration of the infection continuing up to more than a year or two. Although the lesions can resolve without scarring, scratching or physically removing the lesions should be avoided. In some cases, the lesions may cause disfigurement and persisting for 3 to 5 years although reports of recurrences occurring among one-third individuals were witnessed. Among the HIV patients, the lesions can be generalized developing with low counts of CD4 and hence the natural-healing process is rare.
Complications of molluscum contagiosum
Some of the complications of MC include secondary bacterial infection, disseminated secondary eczema, numerous and widespread mollusca among immunocompromised individuals or patients with immune-suppressing medications and scarring because of surgical treatment.
References
http://www.odermatol.com/odermatology/20153/3.Pathogenesis-SharquieKS.pdf
https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0013007/
https://www.cdc.gov/poxvirus/molluscum-contagiosum/treatment.html
https://www.ncbi.nlm.nih.gov/books/NBK441898/
https://www.cdc.gov/poxvirus/molluscum-contagiosum/
https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0076107/
https://www.ncbi.nlm.nih.gov/pubmed/12358555
http://ispub.com/IJD/8/2/11159
https://jamanetwork.com/journals/jamadermatology/fullarticle/1351941