Dermatology · Viral Exanthems
The facts most likely to be tested
Molluscum contagiosum is caused by the Poxvirus family, specifically the Molluscipoxvirus.
The classic clinical presentation is dome-shaped, umbilicated, flesh-colored papules.
Histopathology reveals pathognomonic Molluscum bodies (Henderson-Paterson bodies), which are eosinophilic cytoplasmic inclusions.
Transmission occurs via direct skin-to-skin contact, fomites, or autoinoculation.
In sexually active adults, lesions are typically found in the genital region and are considered a sexually transmitted infection.
Patients with atopic dermatitis are at increased risk for widespread infection due to a compromised skin barrier.
Diagnosis is primarily clinical, and lesions are typically self-limiting in immunocompetent individuals.
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A 5-year-old boy is brought to the clinic by his mother due to a persistent skin rash. Physical examination reveals multiple 2-5 mm dome-shaped, flesh-colored papules with central umbilication scattered across the trunk and axillae. The child has a history of atopic dermatitis. There are no signs of secondary bacterial infection or systemic symptoms.
What is the most likely diagnosis?
Molluscum contagiosum
The diagnosis is based on the classic appearance of umbilicated papules, which is a hallmark feature of Molluscum contagiosum (Bet 2).
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Etiology / Epidemiology
Caused by Poxvirus; common in children, sexually active adults, and immunocompromised patients.
Clinical Manifestations
Painless, umbilicated papules with central caseous plug; pathognomonic Henderson-Paterson bodies.
Diagnosis
Clinical diagnosis; skin biopsy (if uncertain) shows intracytoplasmic inclusions.
Treatment
Self-limiting; curettage or cryotherapy for persistent lesions.
Prognosis
Spontaneous resolution within 6-18 months; scarring is rare.
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Epidemiology & Etiology
Caused by the Molluscum contagiosum virus, a double-stranded DNA Poxvirus. Transmission occurs via direct skin-to-skin contact, fomites, or autoinoculation. It is highly prevalent in children and is considered a sexually transmitted infection in adults.
Pertinent Anatomy
Lesions can appear anywhere on the skin except the palms and soles. In adults, distribution is often limited to the genital region, inner thighs, and lower abdomen.
Pathophysiology
The virus infects keratinocytes, leading to epidermal hyperplasia. The hallmark is the formation of large, eosinophilic, intracytoplasmic inclusion bodies known as Henderson-Paterson bodies that displace the host cell nucleus.
Clinical Manifestations
Presents as discrete, firm, dome-shaped, umbilicated papules. Lesions are typically 2-5 mm in diameter and may exhibit a central caseous plug if expressed. Red flag: Widespread or giant lesions in adults may indicate underlying HIV/AIDS or severe immunosuppression.
Diagnosis
Diagnosis is primarily clinical. If the presentation is atypical, a skin biopsy or scraping of the caseous material reveals the pathognomonic Henderson-Paterson bodies on histology or Wright-Giemsa stain.
Treatment
Observation is preferred as the condition is self-limiting. For cosmetic or symptomatic relief, curettage or cryotherapy are standard. Avoid aggressive treatment in children to prevent scarring. Topical cantharidin is an alternative, but do not apply to the face or genitalia due to risk of severe blistering.
Prognosis
Most cases resolve spontaneously within 6-18 months. Secondary bacterial infection is the most common complication; monitor for signs of cellulitis.
Differential Diagnosis
Varicella: pruritic vesicles that crust over
Condyloma acuminatum: cauliflower-like, non-umbilicated
Cryptococcosis: common in HIV, often ulcerated
Basal cell carcinoma: pearly papule with telangiectasias
Folliculitis: inflammation centered around hair follicles