Dermatology MCQ - Viral Infections - Molluscum Contagiosum

A 4-year-old boy presents with multiple, discrete, flesh-colored, dome-shaped papules with central umbilication in the axillae and antecubital fossae. His mother reports he has a history of atopic dermatitis. Which of the following is the most accurate description of the viral pathogen responsible for this condition?

A) A double-stranded DNA poxvirus transmitted through direct skin-to-skin contact
B) A single-stranded RNA paramyxovirus transmitted via respiratory droplets
C) A double-stranded DNA herpesvirus that establishes latency in sensory ganglia
D) A single-stranded RNA parvovirus that causes a "slapped cheek" rash
E) A single-stranded RNA picornavirus transmitted by the fecal-oral route

Correct Answer: A) A double-stranded DNA poxvirus transmitted through direct skin-to-skin contact

Explanation

This presentation is classic for molluscum contagiosum, a common viral skin infection.

Key Clinical Features:

• Presentation: Flesh-colored or pearly, dome-shaped umbilicated papules.

• Distribution: Often in areas of skin-to-skin contact (axillae, antecubital fossae, groin). In children, lesions are frequently on the trunk, face, and extremities.

• Association with Atopic Dermatitis: Children with atopic dermatitis are particularly susceptible to widespread molluscum due to compromised skin barrier function and immune dysregulation.

Virologic Features:

• Causative Agent: Molluscum contagiosum virus (MCV).

• Virus Family: MCV is a double-stranded DNA virus belonging to the Poxviridae family. It is the only poxvirus that exclusively infects humans.

• Transmission: Primarily through direct skin-to-skin contact or fomite transmission (e.g., towels, swimming pools). Autoinoculation is common.

Why Not the Other Options?

• (B) Single-stranded RNA paramyxovirus: This describes viruses like measles or mumps, which cause systemic illnesses with febrile prodromes and diffuse rashes, not localized umbilicated papules.

• (C) Double-stranded DNA herpesvirus: Herpesviruses (e.g., HSV, VZV) cause vesicular eruptions, pain, and establish latency. Molluscum lesions are non-painful papules without latency.

• (D) Single-stranded RNA parvovirus: Parvovirus B19 causes erythema infectiosum ("fifth disease"), characterized by a "slapped cheek" rash and a lacy reticular exanthem, not umbilicated papules.

• (E) Single-stranded RNA picornavirus: Picornaviruses include enteroviruses (e.g., coxsackievirus), which cause hand, foot, and mouth disease (vesicles on palms/soles/oral mucosa), not umbilicated papules.

Histopathology:

• Biopsy reveals molluscum bodies (large, eosinophilic cytoplasmic inclusions) in the epidermis, which push the nucleus to the side. These are filled with viral particles.

Management:

• Observation: Often self-resolves within 6-18 months as immunity develops.

• Destructive Therapies: Cryotherapy, curettage, or cantharidin may be used for bothersome or widespread lesions.

• Address Atopic Dermatitis: Improving skin barrier function with emollients and anti-inflammatory treatments can reduce spread and new lesions.

Prognosis: Excellent; lesions resolve without scarring unless secondarily infected or aggressively treated.