Emergent itchy rash in a 5-year-old boy

The case

A healthy 5-year-old boy with a 6-month history of asymptomatic 2-mm to 3-mm papules on his legs presents for evaluation of a red, slightly itchy rash that just developed on the back of his right knee.

Diagnosis: Molluscum ID or Dermatitis

Clinical findings

Molluscum contagiosum (MC) is a self-limited pox-virus infection of the skin usually spread through direct skin-to-skin contact of the involved area or autoinoculation.¹ The lesions usually present as 1-mm to 3-mm pale or skin-colored papules with central umbilication and commonly arise in the face, extremities, and trunk regions.^2,3 In many cases, the MC lesions can become inflamed and surrounded by eczematous dermatitis known as molluscum dermatitis or “id” reaction (Figure).

Epidemiology/Etiology

Whereas the manifestation of molluscum dermatitis is well recognized, the prevalence has not been well characterized. Across 6 studies examining molluscum dermatitis in MC patients, the prevalence ranged from 9% to 39%.² It may actually be higher because it is often a harbinger of regression, and there may be a bias of ascertainment as many cases may go undocumented.

Currently, the exact cause of an id reaction in molluscum contagiosum is unknown.⁴ However, it has been suggested that it may be a T-cell–mediated, delayed-hypersensitivity reaction that represents an immunologic response to the virus, leading to inflammation of the MC lesion and an eczematous rash.¹ This hypothesis is supported by biopsies of molluscum dermatitis areas that have revealed the presence of molluscum bodies and an eczematous inflammatory infiltrate in the dermis.³

Risk factors for developing MC include frequent use of public pools or baths, male gender, residence in tropical climates, and immunosuppression. Previous studies have suggested that children with atopic dermatitis are at a greater risk of developing MC, but more recent studies have failed to find atopic dermatitis to be a risk factor for the development of MC. Molluscum id reactions manifest in both atopic and nonatopic individuals.⁴

Differential diagnosis

The diagnosis of MC is usually made by examination of the skin, although scraping or performing a biopsy, which is usually unnecessary, can help confirm the diagnosis.¹ Examination with a dermatoscope or magnifier can easily help to confirm the diagnosis quickly, and siblings or other close friends often have a recent history of MC.

Treatment and management

Molluscum contagiosum usually resolves on its own within a few months to years. Therefore, if an individual is asymptomatic, the progression of the infection should be observed. Emollients may be used and topical antibiotics as well if the lesions become infected. However, if an individual is symptomatic, then treatment for the symptoms may be beneficial. For instance, in cases of severe pruritis, a short course of topical corticosteroids may be used but long-term use should be discouraged as it may delay resolution of the viral infection.⁴

There is little evidence that aggressive destructive measures are effective, and these may result in scarring. Furthermore, when comparing resolution of MC in treated versus untreated patients, a study found that treatment did not shorten the course of infection.⁵

Patient outcome

Because this patient complained only of mild pruritus, clinicians recommended emollients and a low-potency topical steroid when symptoms flared. He also was given topical mupirocin ointment for use only for signs of secondary infection. The family was reassured that the “id” reaction was a harbinger of MC resolution, and MC and the dermatitis cleared over the next 2 months.^1,4

References:

1. Schaffer JV, Berger EM. Molluscum contagiosum. JAMA Dermatol. 2016;152(9):1072.

2. Berger EM, Orlow SJ, Patel RR, Schaffer JV. Experience with molluscum contagiosum and associated inflammatory reactions in a pediatric dermatology practice: the bump that rashes. Arch Dermatol. 2012;148(11):1257-1264.

3. Kipping HF. Molluscum dermatitis. Arch Dermatol. 1971;103(1):106-107.

4. Netchiporouk E, Cohen BA. Recognizing and managing eczematous id reactions to molluscum contagiosum virus in children. Pediatrics. 2012;129(4):e1072-e1075.

5. Basdag H, Rainer BM, Cohen BA. Molluscum contagiosum: to treat or not to treat? Experience with 170 children in an outpatient clinic setting in the northeastern United States. Pediatr Dermatol. 2015;32(3):353-357.