This atypical lesion might warrant a biopsy. However, upon closer examination, you can appreciate a small papule with a whitish center, at the inferior margin of the tumor (6 o’clock), and another flat-topped papule with a white center several centimeters inferior-lateral to the lesion, both consistent with molluscum lesions. Therefore, the tumor is consistent with a giant molluscum contagiosum.
Molluscum contagiosum is a cutaneous viral infection caused by the poxvirus, which commonly affects children. It can spread easily by direct physical contact, fomites, and autoinoculation.1 It usually presents with skin-colored or pink pearly dome-shaped papules with central umbilication that can occur anywhere on the face or body. The skin lesions can be asymptomatic or pruritic. When the size of the molluscum is 0.5 cm or more in diameter, it is considered a giant molluscum. Atypical size and appearance may be seen in patients with altered or impaired immunity such as those with HIV.2,3 Giant molluscum has been reported in immunocompetent patients as well.4,5
The diagnosis of molluscum contagiosum usually is made clinically. Our patient had typically appearing molluscum lesions approximate to the larger lesion of concern. She was overall healthy without any history of impaired immunity so no further work-up was pursued. However, a biopsy of the skin lesion may be considered if the diagnosis is unclear.
What’s the treatment plan?
Treatment may not be necessary for molluscum contagiosum because it is often self-limited in immunocompetent children, although it can take many months to years to resolve. Treatment may be considered to reduce autoinoculation or risk of transmission because of close contact to others, to alleviate discomfort, including itching, to reduce cosmetic concerns and to prevent secondary infection.6
The most common treatments for molluscum contagiosum are cantharidin or cryotherapy. Other treatment available include topical retinoids, immunomodulators such as cimetidine, or antivirals such as cidofovir.1 Lesions with or without treatment may exhibit the BOTE (beginning of the end) sign, which is an apparent worsening associated with the body’s immune response to the molluscum virus and generally indicates imminent resolution.
What’s the differential diagnosis?
The differential diagnosis for giant molluscum contagiosum includes epidermal inclusion cyst, skin tag, pilomatrixoma, and amelanotic melanoma.
Epidermal inclusion cyst typically presents as a firm, mobile nodule under the skin with central punctum, which can enlarge and become inflamed. It can be painful, especially when infected. Definitive treatment is surgical excision because it rarely resolves spontaneously.
Skin tags, also known as acrochordons, are benign skin-colored papules most often found in the skin folds. People with obesity and type 2 diabetes are at higher risk for skin tags. Skin tags may be treated with cryotherapy, surgical excision, or ligation.
Pilomatrixoma is a benign skin tumor derived from hair matrix cells. It is usually a nontender, firm, skin-colored or red-purple subcutaneous nodule that may have calcifications. Treatment is surgical excision.
Amelanotic melanoma is a melanoma with little or no pigment and can present as a skin- or red-colored nodule. While these are quite uncommon, recognition that many pediatric melanomas present as amelanotic lesions makes it important to consider this in the differential diagnosis of growing papules and nodules.7 Treatment and prognosis is similar to that of pigmented melanoma, but as it is often clinically challenging to diagnose because of atypical features, it may be detected in more advanced stages.
Our patient underwent cryotherapy with liquid nitrogen to the nodule given the large size of the lesion, with resolution without recurrence.
Dr. Lee is a pediatric dermatology research fellow in the division of pediatric and adolescent dermatology at the University of California, San Diego and Rady Children’s Hospital–San Diego. Dr. Eichenfield is chief of pediatric and adolescent dermatology at Rady Children’s Hospital–San Diego. He is vice chair of the department of dermatology and professor of dermatology and pediatrics at the University of California, San Diego. Neither Dr. Lee nor Dr. Eichenfield had any relevant financial disclosures. Email them at [email protected].
6(Itasca, Ill.: American Academy of Pediatrics, 2018, pp. 565-66).