Molluscum Contagiosum

Molluscum contagiosum is a common, viral skin infection caused by a poxvirus. It is benign but highly contagious.

• Onset: Patients report the gradual appearance of small, "pearly" bumps over several weeks.

• Transmission: 

  • Children: Spreads via direct skin-to-skin contact, sharing towels, or in communal settings like swimming pools or contact sports.

  • Adults: Often considered a sexually transmitted infection (STI) when found in the genital region, following intimate contact.

• Symptoms: Usually painless and asymptomatic. However, as the body’s immune system begins to recognize the virus, the bumps may become itchy, red, or irritated (often called the "Beginning of the End" sign).

• Risk Factors: Significantly more extensive or persistent in patients with Atopic Dermatitis (Eczema) or immunosuppression (e.g., HIV/AIDS).

Diagnosis is clinical and based on the unique "umbilicated" morphology of the lesions.

• Morphology: Small (2–5 mm), firm, dome-shaped papules that are typically flesh-colored, white, or pearly.

• Pathognomonic Sign: A tiny central dimple (umbilication) is often visible, especially with a magnifying glass or dermatoscope.

• Distribution: 

  • Children: Face, trunk, and extremities.

  • Adults: Lower abdomen, groin, and thighs.

• Molluscum Dermatitis: A dry, pink, eczematous patch may develop around the lesions as the immune system reacts to the virus.

Crucial Note for Darker Skin Tones

• Color Variation: In darker skin, the lesions may not appear "pearly pink." Instead, they often present as hyperpigmented (dark brown/black) or even hypopigmented (lighter than surrounding skin) nodules.

• Post-Inflammatory Changes: As the lesions resolve, they frequently leave behind Post-Inflammatory Hyperpigmentation (PIH). These dark spots can last for several months, and patients should be reassured that this is not a recurrence of the virus.

• Differential Diagnosis:

  • Cryptococcosis/Histoplasmosis: In severely immunocompromised patients, deep fungal infections can mimic the umbilicated look of molluscum but are a medical emergency.

  • Adnexal Tumors: Small skin-colored bumps like syringomas or trichoepitheliomas may look similar but lack the central dimple and sudden onset.

While molluscum contagiosum is self-limiting and may resolve within 6–12 months, treatments can aid in symptom management and reduce transmission risk:

1. Topical Therapies:

   • Cantharidin (0.7% solution) can be applied to lesions in the clinic, causing blistering and destruction of lesions. Treatment is applied every 3–4 weeks until lesions resolve.

   • Tretinoin cream (0.025% or 0.05%), applied at night, may help but may cause irritation, especially on sensitive skin.

2. Cryotherapy: Liquid nitrogen application every 2–3 weeks can effectively freeze and destroy lesions. This may require multiple sessions and can occasionally cause hypopigmentation in darker skin tones.

3. Oral Medications:

   • Cimetidine (20–40 mg/kg per day), although used off-label, has shown promise, especially for children with widespread lesions.

4. Laser Therapy: Pulse dye laser treatments are available but often reserved for resistant or cosmetically concerning cases.

5. Prevention: Advise on avoiding skin-to-skin contact in affected areas to limit spread, especially in communal environments.

Risk Factors, Prognosis, and Complications

Prognosis is favorable, with most cases resolving within a year. Complications include secondary bacterial infections or post-inflammatory hyperpigmentation, especially in Black patients following lesion resolution or inflammation.

Darker Skin Tones – Specific Treatment Risks:

• Pigmentation Risk: Destructive treatments like cryotherapy or strong chemicals carry a high risk of leaving permanent white spots (hypopigmentation) or dark scars (hyperpigmentation). For many patients with darker skin, "watchful waiting" is often the safest cosmetic choice.

• Eczema Management: If the patient has underlying atopic dermatitis, treating the eczema with mild steroids can actually help the molluscum clear faster by restoring the skin barrier, provided it's done under supervision.

• DermNet NZ – Molluscum Contagiosum: https://dermnetnz.org/topics/molluscum-contagiosum

• StatPearls – Molluscum Contagiosum (2024 update): https://www.ncbi.nlm.nih.gov/books/NBK442003/

• CDC – Molluscum Contagiosum Risk & Prevention: https://www.cdc.gov/poxvirus/molluscum-contagiosum/index.html